atmosphere

Article Understanding Spatial Variability of Air Quality in : Part 1—A Suburban Balcony Case Study

Jack B. Simmons 1 , Clare Paton-Walsh 1,* , Frances Phillips 1 , Travis Naylor 1, Élise-Andrée Guérette 1 , Sandy Burden 1, Doreena Dominick 1, Hugh Forehead 1 , Joel Graham 1, Thomas Keatley 1, Gunaratnam Gunashanhar 2 and John Kirkwood 2

1 Centre for Atmospheric Chemistry, University of Wollongong, Wollongong, 2522, Australia; [email protected] (J.B.S.); [email protected] (F.P.); [email protected] (T.N.); [email protected] (É.-A.G.); [email protected] (S.B.); [email protected] (D.D.); [email protected] (H.F.); [email protected] (J.G.); [email protected] (T.K.) 2 New South Wales Office of Environment and Heritage, Sydney, New South Wales 2000, Australia; [email protected] (G.G.); [email protected] (J.K.) * Correspondence: [email protected]; Tel.: +61-2-4221-5065

 Received: 25 February 2019; Accepted: 2 April 2019; Published: 4 April 2019 

Abstract: There is increasing awareness in Australia of the health impacts of poor air quality. A common public concern raised at a number of “roadshow” events as part of the federally funded Clean Air and Urban Landscapes Hub (CAUL) project was whether or not the air quality monitoring network around Sydney was sampling air representative of typical suburban settings. In order to investigate this concern, ambient air quality measurements were made on the roof of a two-storey building in the Sydney suburb of Auburn, to simulate a typical suburban balcony site. Measurements were also taken at a busy roadside and these are discussed in a companion paper (Part 2). Measurements made at the balcony site were compared to data from three proximate regulatory air quality monitoring stations: Chullora, Liverpool and Prospect. During the 16-month measurement campaign, observations of carbon monoxide, oxides of nitrogen, ozone and particulate matter less than 2.5-µm diameter at the simulated urban balcony site were comparable to those at the closest permanent air quality stations. Despite the Auburn site experiencing 10% higher average carbon monoxide amounts than any of the permanent air quality monitoring sites, the oxides of nitrogen were within the range of the permanent sites and the pollutants of greatest concern within Sydney (PM2.5 and ozone) were both lowest at Auburn. Similar diurnal and seasonal cycles were observed between all sites, suggesting common pollutant sources and mechanisms. Therefore, it is concluded that the existing air quality network provides a good representation of typical pollution levels at the Auburn “balcony” site.

Keywords: PM2.5; ozone; fine particulate pollution; urban air quality; traffic emissions

1. Introduction Air quality in Sydney is relatively good compared to other large industrialised cities [1]. Background ozone concentrations in Sydney are comparatively low: the annual mean ozone concentration for Sydney was 18.5 ppb in 2017 [2]. In comparison, the 2017 mean ozone concentration for urban sites in the UK was 27.9 ppb [3]. In New South Wales (NSW), measured particulate matter −3 (<2.5 µm diameter; PM2.5) concentrations are generally <15 µgm , but occasionally exceed the national daily standard (25 µgm−3) particularly during wildfire events [4]. Despite the relatively low levels of harmful air pollutants measured in Sydney, air quality constitutes a health risk in the city. It has been established that exposure to some pollutants, including ozone and PM2.5, at concentrations

Atmosphere 2019, 10, 181; doi:10.3390/atmos10040181 www.mdpi.com/journal/atmosphere Atmosphere 2019, 10, 181 2 of 18 considered generally safe by the US EPA is nevertheless associated with negative health outcomes [5,6]. Furthermore, approximately 2% of deaths in Sydney have been attributed to ozone and particulate pollution [1]. These species dominate exceedances of national air quality standards in Sydney [2,7]. Ozone and particulate matter have therefore been identified as pollutants of most concern in Sydney. Ozone exceedances in Sydney are associated with very high summer temperatures, with influence from both synoptic [8] and mesoscale [9] meteorological variables. The Sydney region predominantly experiences a NOx-limited regime during ozone events, with the influence of biogenic emissions highlighted in recent literature [10]. Despite the strong influence of bushfires and dust storms on PM2.5 exceedances [11,12], traffic emissions have been shown to be the largest single source of PM2.5 within the Sydney basin [13]. Methods used to gather ambient air quality data largely utilise fixed-site ground-level monitoring stations often located in local parks that measure background pollutant concentrations. For example, the New South Wales Office of Environment and Heritage (OEH) maintains a network of permanent, stationary air quality monitoring stations throughout Sydney [2]. Increasing population in Sydney is driving increased construction of (and residence in) apartment buildings. Apartment buildings accounted for one-third of all new residential building approvals in Australia in 2015, with more than 30% of these in Sydney [14]. As of the 2016 census, 20.7% of residences in New South Wales were apartments, with greater than 85% of these apartments located in Sydney [15]. Therefore, it is reasonable to assume that urban balconies are a site of possible exposure to poor air quality for a significant proportion of the population of Sydney. A small body of research exists discussing the effect of balconies on ventilation impacting indoor air quality in high rise buildings [16,17] and regarding pollutant mixing in urban street canyons [18]. However, limited research exists regarding air quality measurements at balcony sites. Nevertheless, general research into vertical changes in urban air quality has been more thoroughly researched. Ozone has been modelled to vary with height above street level. The presence of other ozone-destroying compounds in urban areas is modelled to deplete surface ozone up to altitudes of 20 m [19]. This phenomenon has been measured in Beijing [20], with the effect of shears in wind speed and wind direction highlighted. Several studies have found that PM2.5 concentrations decrease with increased height in an urban environment [21,22]. Contrastingly, a study on multi-storey buildings in Singapore showed that mean PM2.5 concentration was highest at the mid-floors in comparison to upper and lower floors, and the upper floors had the lowest fine particular matter mass concentration [23]. It was noted, however, that this may have been the result of particle interception by surrounding tree leaves and inflow of cleaner air from higher altitudes. Han et al. [24] found that measurement sites at near-ground height (5–10 m) were most influenced by human emission activities compared to measurements at higher altitudes. It has been noted that a number of factors influence the vertical profiles of PM2.5 concentrations, including vehicle emissions and new particle formation [25]. Urban street canyons and the presence of neighbouring buildings have also been shown to play a role by altering vertical mixing and flow fields [18]. The Clean Air and Urban Landscapes (CAUL) hub is a project of the National Environmental Science Program, which is funded by Australia’s Department of the Environment and Energy. CAUL focuses on cross-disciplinary research on the sustainability and liveability of Australian urban environments [26]. Air quality is an important part of this investigation. CAUL research is partially driven by public concerns expressed at a number of “roadshow” events. A recurring question posed by members of the public was “how does the background air quality reported for my area relate to my likely exposure when I am outside?” Although we acknowledged that we cannot answer this question for any particular individual, we nevertheless set about trying to address this problem via the use of two separate case studies:

1. WASPSS-Auburn (Western Air-Shed Particulate Study for Sydney in Auburn)—provides an assessment of whether the local air quality monitoring stations give a good representation of pollutant concentrations at a site representative of a suburban balcony setting. Atmosphere 2019, 10, 181 3 of 18

2. The RAPS campaign (Roadside Atmospheric Particulates in Sydney) provides an assessment of PM2.5 concentrations near a busy road in the Sydney City metropolitan area, and how these compare to reported air quality levels from nearby statutory monitoring stations. The spatial and temporal variability of PM2.5, relevant to members of the public seeking to minimise their exposure to fine particulate matter, are also explored. The campaign also provided an opportunity for the first calibration of a microscopic traffic emissions simulation. The first case study is discussed in the present paper, and the second is covered in a companion paper, also in this issue [27]. The WASPSS-Auburn campaign incorporated a mobile air quality monitoring station and an open-path infrared Fourier transform spectrometer (OP-FTIR). The OP-FTIR system, which can measure infrared active gases such as CO, NH3,N2O and CH4, has previously been deployed for agricultural [28–30] and biomass burning [31,32] emissions estimates. Details of the main findings from the OP-FTIR during WASPSS, which relate to vehicle ammonia emissions and episodes of significant smoke pollution, are presented in two separate papers [33,34]. In this paper we present the results from the mobile air quality monitoring station during the 16-month WASPSS-Auburn campaign at the simulated suburban balcony site and compare the pollution levels observed to those measured at the closest permanent air quality monitoring stations. Local-scale phenomena, including the built environment and meteorological processes, dominate vertical variability in urban pollutant concentrations, especially particulates and ozone, making it very difficult to generalise findings at any one site to a broader region; however this is not the purpose of this study. Instead, we aim to observe the similarities and differences between pollutant concentrations at a simulated urban balcony site and regional air quality monitoring stations and test the assumption that regional background measurements provide a reasonable representation of pollutant concentrations to which local residents may be exposed to on an urban balcony.

2. Methodology

2.1. The Mobile Air Quality Station The Mobile Air Quality station (MAQ) (inset, Figure1) is a mobile compact air quality station that complies with the Australian/New Zealand Standards for the measurement of ambient air quality, National Environmental Protection (Ambient Air Quality) Measure (NEPM) [35]. The MAQ is fitted with the following instruments.

• Model T204 Teledyne NOx + O3 Analyser • Model T300 Teledyne CO Analyser

• Model 100E Teledyne SO2 Analyser • Thermo Scientific TEOM Series Model 1405-DF (used for reported PM2.5 and PM10 measurements) • Ecotech Aurora 3000 multi wavelength integrating Nephelometer • Met-One 50.5 sonic wind sensor • Vaisala HMP155 Temperature and Humidity Sensor Calibration and communications equipment was also installed, allowing quality control and monitoring of the instrumentation. Measurements were taken at one-minute time resolution and averaged to one hour mean values. Maintenance and calibration were performed in accordance with Climate and Atmospheric Science Standard of Operation Procedures [36]. Note that all observations described in this paper are from the MAQ station unless explicitly stated otherwise. Further details on the measurements are publicly available [37].

2.2. Auburn Balcony Measurement Site Auburn is a suburb in Western Sydney that is located 16 km west of downtown Sydney (measured from ) containing residential, business and industrial areas, as well as numerous Atmosphere 2019, 10, 181 4 of 18 parks and sporting complexes. On the 23 May 2016 the MAQ station was placed on site on the roof of the second storey of a commercial business at 2 Percy Street, Auburn, (33.854690◦ S, 151.037400◦ E, Atmosphere 2018, 9, x FOR PEER REVIEW 4 of 19 6.72 m above ground level, 20.6 m above sea level). This site was chosen purely for pragmatic reasons, aspurely we had for connections pragmatic toreasons, allow usas accesswe had to theconnections roof (and gainedto allow permission us access to to locate the roof the retroreflectors (and gained forpermission the open-path to locate measurements the retroreflectors on the councilfor the buildingopen-path 400 measurements m away across on the the town council centre). building However, 400 Auburnm away isacross a good the representative town centre). suburban However, centre Auburn with is a gooda good mixture representative of land uses suburban including centre residential, with a industrialgood mixture and of transport. land uses The including MAQ inlet residential, height was industrial 3.3 m above and thetransport. rooftop. The The MAQ Auburn inlet site height (Figure was1 main3.3 m image) above is the adjacent rooftop. to a majorThe Auburn rail passageway, site (Figure with 1 several main industrialimage) is sites adjacent in the vicinity.to a major There rail is apassageway, nearby major with intra-urban several industrial road (A6) sites situated in the 330 vicinity. m to the There east is of a thenearby site withmajor the intra-urban Great Western road highway(A6) situated (A44) 330 and m the to M4the motorway,east of the also site runswith from the Great north toWestern east, at highway distances (A44) of just and over the 2 kmM4 frommotorway, the site. also Measurements runs from north are availableto east, at from distance 26 Mays of 2016just over until 2 18 km September from the 2017.site. Measurements Data from the MAQare available and from from the 26 Open May Path 2016 FTIR until and 18 September associated 2017. instruments Data from are availablethe MAQ atand the from Pangaea the Open Data PublisherPath FTIR [and37]. associated instruments are available at the Pangaea Data Publisher [37].

Figure 1.1. Inset-The mobile air qualityquality stationstation (MAQ)(MAQ) inin positionposition atat thethe AuburnAuburn balconybalcony site.site. MainMain imageimage mapmap indicatingindicating thethe positionposition ofof thethe MAQMAQ (blue(blue pin)pin) andand thethe surroundingsurrounding roads.roads. LocationLocation of Silverwater Road (north) and OlympicOlympic Drive (south) traffictraffic counters areare indicatedindicated byby greygrey pins.pins. Note thethe presencepresence ofof thethe majormajor A6A6 roadroad 330330 mm easteast ofof thethe site.site. GeneratedGenerated inin OpenStreetMapOpenStreetMap ®®..

2.3. Chullora, Prospect and Liverpool Air Quality Monitoring StationsStations The OEH monitors air quality in urban areas of New South Wales using strategically placed air quality monitoring stations. These These sites are equipped with instrumentation sufficient sufficient to meet the AmbientAmbient Air Quality NEPM [[38],38], with measurements taken using a standard sampling protocol and undergoing rigorous quality assurance [[39].39]. Instrumentation at permanent sites is different to thatthat used in thethe MAQMAQ station,station, withwith specificationsspecifications forfor eacheach sitesite beingbeing publiclypublicly availableavailable [[40].40]. ThisThis allowsallows the OEHOEH toto provideprovide currentcurrent datadata onlineonline publicly and allows for comparison between network sites. sites. Measurements taken at the Auburn balcony site were compared with the following three air quality monitoring stations inin westernwestern Sydney:Sydney: Chullora, Liverpool andand Prospect.Prospect.

1.1. ChulloraChullora air air quality monitoring station (33°53’38 (33◦53038’’00 S,S, 151°02’43’’ 151◦0204300 E, 32 m above sea level), is locatedlocated in in the the grounds grounds of of the the Southern Southern Sydney Sydney TAFE, TAFE, Worth St, Chullora, in a mixed residential andand commercial commercial area. Nearby Nearby traffic traffic influences influences include the A6 and , both within 0.50.5 km km from from the site and with a major road joining the two approximately 150 m to the south. 2. Liverpool air quality monitoring station (33°55’58’’ S, 150°54’21’’ E, 22 m above sea level) is located in the Council depot, off Rose Street, Liverpool, in a mixed residential and commercial area. The Hume Highway and are both within approximately 1 km of the site. 3. Prospect air quality monitoring station (33°47’41’’ S, 150°54’45’’ E, 66 m above sea level) is located in William Lawson Park, Myrtle Street, Prospect, in a residential area. The lies approximately 1 km to the south, with the a further 400 m south.

Atmosphere 2019, 10, 181 5 of 18

2. Liverpool air quality monitoring station (33◦5505800 S, 150◦5402100 E, 22 m above sea level) is located in the Council depot, off Rose Street, Liverpool, in a mixed residential and commercial area. The Hume Highway and M5 motorway are both within approximately 1 km of the site. 3. Prospect air quality monitoring station (33◦4704100 S, 150◦5404500 E, 66 m above sea level) is located in William Lawson Park, Myrtle Street, Prospect, in a residential area. The Great Western Highway lies approximately 1 km to the south, with the M4 motorway a further 400 m south. Atmosphere 2018, 9, x FOR PEER REVIEW 5 of 19 These sites were selected as they are the most proximate stations (within 15 km) to the Auburn These sites were selected as they are the most proximate stations (within 15 km) to the Auburn site, located to the southwest, southeast and northwest, respectively (Figure2). Each of these stations site, located to the southwest, southeast and northwest, respectively (Figure 2). Each of these stations is located in or adjacent to reserves of parklands. Publicly available hourly measurements from each is located in or adjacent to reserves of parklands. Publicly available hourly measurements from each air qualityair quality monitoring monitoring station station were were downloaded downloaded fromfrom the OEH OEH website website [41]. [41 ].

FigureFigure 2. Map 2. Map showing showing the the around around the the WASSPS-Auburn WASSPS-Auburn campaign campaign site site (indicated (indicated by the by blue the bluepin), pin), includingincluding surrounding surrounding air qualityair quality monitoring monitoring stations stations (yellow (yellow pins),pins), genera generatedted using using Google Google Earth Earth ®. ®. 2.4. Traffic Counters 2.4. Traffic Counters Measurements from two traffic counters, located on Olympic Drive (station 7153, 1.25 km SSE Measurements from two traffic counters, located on Olympic Drive (station 7153, 1.25 km SSE of Auburn balcony) and on Silverwater Road (station 7112, 1.40 km NNE of Auburn balcony), were of Auburn balcony) and on Silverwater Road (station 7112, 1.40 km NNE of Auburn balcony), were used to assist with pollutant analysis (see Figure1 for locations). Traffic counters are maintained by used to assist with pollutant analysis (see Figure 1 for locations). Traffic counters are maintained by the Newthe New South South Wales Wales Roads Roads and and Maritime Maritime Services. Services. Hourly Hourly measurements measurements of total of total vehicle vehicle count count fromfrom 26 May 26 2016May 2016 to 13 to September 13 September 2017 2017 were were downloaded downloaded for for each each site site and and processed processed to meanto mean hourly countshourly during counts the during measurement the measurement period. Bothperiod. cameras Both cameras count count traffic traffic travelling travelling northbound northbound on on the A6. Datathe is publicly A6. Data availableis publicly from available the Roadsfrom the and Roads Maritime and Maritime Services Services website website [42]. [42].

2.5. Data2.5. Data Analysis Analysis VariablesVariables selected selected for for analysis analysis were were wind wind speed,speed, temperature, carbon carbon monoxide monoxide (CO), (CO), oxides oxides of of nitrogen (NOx), ozone (O3) and PM2.5. Meteorological variables were chosen to account for the effect nitrogen (NOx), ozone (O3) and PM2.5. Meteorological variables were chosen to account for the effect of temperature and wind speed on pollutant concentrations. Ozone and PM2.5 have been identified of temperature and wind speed on pollutant concentrations. Ozone and PM2.5 have been identified as pollutants of most concern in Sydney and were therefore critical to the project. CO and NOx were as pollutants of most concern in Sydney and were therefore critical to the project. CO and NO were analysed as they are associated with traffic emissions and interact with and influence concentrationsx analysedof the as pollutants they are associatedof most concern. with traffic emissions and interact with and influence concentrations of the pollutantsData ofwere most analysed concern. using the software “R” (version 3.4.0) [43] making extensive use of the Data“openair” were package analysed (version using 2.6.1) the software[44]. Mean “R” statistics (version reported 3.4.0) refer [43] to making the entire extensive measurement use of the “openair”campaign. package Mean (version bias values 2.6.1) were [44 calculated]. Mean using statistics the openAir reported “modStats” refer to thepackage entire [44] measurement and are campaign.expressed Mean as a biaspercentage values of were the overall calculated mean valu usinge for the the openAir variable “modStats”at the Auburn package balcony site. [44 ] and are expressedThe as apercentage percentage of ofvalid the data overall collected mean over value the for measurement the variable period at the Auburnwas as follows balcony for site. the analysed variables; temperature and wind speed: 100%; CO: 94%; NOx: 78%; O3: 60.1%; PM2.5 and PM10; 99%.

3. Results and Discussion

Atmosphere 2019, 10, 181 6 of 18

The percentage of valid data collected over the measurement period was as follows for the analysed variables; temperature and wind speed: 100%; CO: 94%; NOx: 78%; O3: 60.1%; PM2.5 and PM10; 99%.

3. Results and Discussion Atmosphere 2018, 9, x FOR PEER REVIEW 6 of 19 Measurements from the Auburn balcony site were compared to the regional background Measurements from the Auburn balcony site were compared to the regional background concentrations as measured by three proximal air quality monitoring stations located at Chullora, concentrations as measured by three proximal air quality monitoring stations located at Chullora, LiverpoolLiverpool and Prospect. and Prospect.

3.1. Wind3.1. andWind Temperature and Temperature ExaminationExamination of wind of wind speed speed measurements measurements revealed revealed that that the the Auburn Auburn balcony balcony has has a diurnala diurnal cycle similarcycle to the similar background to the background sites (Figure sites3A). (Figure At each 3A). location, At each the location, wind speed the wind is lowest speed overnight is lowest and into theovernight morning and (23:00–06:00). into the morning Wind (23:00–06:00). speed then Wi increasesnd speed through then increases the morning, through peaking the morning, between 12:00 andpeaking 18:00, between before 12:00 dropping and 18:00, back before to a minimum dropping lateback in to the a minimum evening. Alllate permanentin the evening. air qualityAll monitoringpermanent sites air display quality higher monitoring wind sites speeds display throughout higher wind the 24-hspeeds cycle throughout than the the balcony 24-h cycle site. than This is −1 reflectedthe bybalcony a lower site. mean This is wind reflected speed by ata Auburnlower mean (1.3 wind ms− speed1) compared at Auburn to Chullora,(1.3 ms ) compared Liverpool to and Chullora, Liverpool and Prospect (1.7, 2.0 and 1.9 ms−1, respectively). The average mean bias Prospect (1.7, 2.0 and 1.9 ms−1, respectively). The average mean bias between Auburn and the air between Auburn and the air quality monitoring stations is −47%. This is likely to be due to the quality monitoring stations is −47%. This is likely to be due to the positioning close to buildings positioning close to buildings dampening the measured wind speed at Auburn, compared to the dampeningmeasurements the measured in more wind open speed areas at at the Auburn, permanent compared air quality to the stations. measurements in more open areas at the permanent air quality stations.

A B 3.0 2.5 ) ) 1 1 − − 2.5 2.0

2.0

1.5

Wind speed (ms speed Wind 1.5 (ms speed Wind

1.0 1.0

0 6 12 18 23 JFMAMJJASOND hour month

C D 22 25

20

18 20

16

Temperature (°C) Temperature (°C) Temperature 15 14

12

0 6 12 18 23 JFMAMJJASOND hour month

FigureFigure 3. Diurnal 3. Diurnal and seasonal and seasonal cycles cycles of mean of mean wind wind speed speed ((A (,BA), and respectively) B, respectively) and temperatureand temperature ((C ,D), respectively)(C and atD, therespectively) Auburn balconyat the Auburn site and balcony three site surrounding and three surrounding air quality monitoringair quality monitoring stations; 95% confidencestations; intervals 95% confidence in the mean intervals are shaded. in the mean are shaded.

Plotting monthly mean wind speeds demonstrates that all sites follow the same annual trend (Figure 3B) containing an autumn minimum in May and an October spring maximum. The

Atmosphere 2019, 10, 181 7 of 18

Plotting monthly mean wind speeds demonstrates that all sites follow the same annual trend (Figure3B) containing an autumn minimum in May and an October spring maximum. The similarity in seasonal cycle between sites is unsurprising considering their relatively close proximity. Lower wind speeds at Auburn are again evident throughout the cycle. Temporal variations in wind direction were also examined. Measurements were binned into four periods—00:00–06:00, 06:00–12:00, 12:00–18:00, and 18:00–00:00—for each site and plotted as wind roses (AppendixA, Figure A1). Winds until 12:00 at all sites were dominated by SW winds at all sites, with a northerly flow also evident at Prospect. Winds appeared more variable in the afternoon and evening with a greater variability in wind direction evident. Variability observed between sites is unsurprising given the sensitivity of local surface winds to the environment immediately surrounding the measurement site. Seasonality is observed in wind direction at all sites. Site specific wind roses, binned by season, are presented in the AppendixA, Figure A2. Spring and summer winds are the most variable at all sites, with noted northerly airflows observed at Chullora, and easterly flows at Liverpool during summer. Southerly and westerly flows dominate winter winds at Auburn, Chullora and Liverpool, with a distinctive NW flow evident during winter at Prospect. Analysis of mean hourly temperature (Figure3C) again reveals a similar cycle at all sites, with minimum temperatures experienced just prior to sunrise, and building to a maximum in the early afternoon. Auburn is slightly warmer overnight and during early hours of the morning than other sites. The average mean temperature bias of the Auburn balcony compared with the air quality monitoring stations is close to 1 ◦C warmer, perhaps due to the thermal retention properties of the concrete Auburn rooftop as compared to the parkland sites of the other air quality monitoring stations. A plot of mean monthly temperatures (Figure3D) displays the expected seasonal cycle at all sites. Temperature is at its highest (close to 25 ◦C) during summer, with the winter minimum temperature experienced in July. Geographical proximity is again responsible for similarity in the seasonal temperature cycle. Again, slightly warmer temperatures are observed at Auburn compared to other sites. This is particularly noticeable in the cooler months.

3.2. Carbon Monoxide, Oxides of Nitrogen and Ozone

3.2.1. Carbon Monoxide

Diurnal and seasonal cycles of CO, NOx and ozone are presented in Figure4. A plot of hourly mean CO mole fraction (Figure4A) displays a bimodal distribution at all sites. CO pollution begins growing at 05:00, reaching a first peak between 07:00 and 08:00. A decrease from this peak gives diurnal minimum concentrations in the early afternoon, coincident with the timing of peak wind speeds (Figure3A). The evening peak grows from near 17:00 to a maximum near 22:00. The mean CO mole fraction measured at Auburn (0.38 ppm) is similar, albeit slightly higher than that measured at Chullora (0.27 ppm) and Liverpool (0.33 ppm). The mean CO mole fraction at Prospect is significantly lower (0.11 ppm), with lower amounts evident throughout the diurnal cycle. This is reflected in the mean bias between Auburn and the air quality monitoring stations as ranging from +10% (compared to Liverpool) to +68% (compared to Prospect). The significantly lower CO mole fractions at Prospect (which is in a residential area) suggest that the commercial activities near the other sites contribute a substantial fraction of the CO pollution at Auburn, Chullora and Liverpool (that are all mixed residential and commercial areas).

3.2.2. Oxides of Nitrogen

Plotting hourly mean mole fractions of oxides of nitrogen (NOx, Figure4C) reveals a similar bimodal distribution at all locations. The first peak occurs between 07:00 and 08:00, with the broader second peak occurring between 19:00 and 22:00. Morning maximum NOx pollution varies between sites from an average of 60 ppb at Liverpool to an average of almost 30 ppb at Chullora. During the Atmosphere 2019, 10, 181 8 of 18

evening peak, NOx pollution levels at the different sites are more similar to each other especially at Auburn, Liverpool and Chullora. The broadening observed in the evening peak is likely to be caused by a coupling of the evening traffic peak and the collapse of the daytime boundary layer. Again, Atmosphere 2018, 9, x FOR PEER REVIEW 8 of 19 hourly NOx mole fractions are consistently lower at Prospect than at the other sites. This is reflected in a significantlyhourly NO greaterx mole fractions mean bias are consistently between Auburn lower at Prospect and Prospect than at (+32%)the other compared sites. This is to reflected Auburn and Chullorain (+6.9%), a significantly and Auburngreater mean and bias Liverpool between Auburn (−5.3%). and Mid-afternoon Prospect (+32%) compared minimum to NOAuburnx pollution and is observedChullora at all sites (+6.9%), in a similarand Auburn manner and toLiverpool minimum (−5.3%). CO Mid-afternoon pollution. minimum NOx pollution is observed at all sites in a similar manner to minimum CO pollution.

A B 0.5 0.5

0.4 0.4

0.3 0.3

0.2 CO CO (ppmv) 0.2 CO (ppmv)

0.1 0.1

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0 6 12 18 23 JFMAMJJASOND hour month

C D 60 40 50

40 30 (ppbv) (ppbv) x x 30 NO NO 20 20

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E F 30 25

25

20 20

(ppbv) (ppbv) 15 3 15 3 O O

10 10

5

0 6 12 18 23 JFMAMJJASOND hour month

Figure 4. Diurnal and seasonal cycles of mean carbon monoxide mole fractions ((A,B), respectively),

oxides ofFigure nitrogen 4. Diurnal ((C,D ),and respectively), seasonal cycles and of ozone mean(( carbonE,F), respectively) monoxide mole at thefractions Auburn (A and balcony B, site and threerespectively), surrounding oxides air qualityof nitrogen monitoring (C and D, stations.respectively), Calibration and ozone of (E the and ozone F, respectively) monitor occurredat the at 13:00–14:00 daily, and hence measurements have been removed. Atmosphere 2018, 9, x FOR PEER REVIEW 9 of 19

AtmosphereAuburn2019 balcony, 10, 181 site and three surrounding air quality monitoring stations. Calibration of the ozone 9 of 18 monitor occurred at 13:00–14:00 daily, and hence measurements have been removed.

3.2.3.3.2.3. Traffic Traffic as as a a Major Major Source Source of of Carbon Monoxide and Oxides of Nitrogen

TheThe similarity similarity in in diurnal diurnal cycles cycles implies implies that that a a common common source source of of CO CO and and NO NOxx dominatesdominates at at all all measuredmeasured locations. ItIt isis suggestedsuggested that that the the diurnal diurnal cycle cycle is relatedis related to morning to morning and eveningand evening rush hoursrush hoursat all sites,at all withsites, high with overnight high overnight concentrations concentratio attributablens attributable to low to boundary low boundary layer conditions layer conditions [45,46]. [45,46].Examining Examining traffic countstraffic counts along this along road this supports road supports this attribution. this attribution. Northbound Northbound traffic alongtraffic thealong A6 the(300 A6 m (300 east m of theeast balcony of the balcony site) shows site) ashows morning a morning peak at peak 06:00–08:00 at 06:00–08:00 at sites bothat sites north both and north south and of souththe Auburn of the balconyAuburn (Figure balcony5). (Figure This aligns 5). This with aligns the morning with the peak morning in CO andpeak NO in xCO. This and suggestion NOx. This is suggestionfurther supported is further by supported examining by polar examining bivariate pola plotsr ofbivariate the Auburn plots balconyof the Auburn site. The balcony slightly site. elevated The slightlypollution elevated levels of pollution CO and NOlevelsx associated of CO and with NO relativelyx associated strong with easterly relatively winds strong (Figure easterly6A,B) is winds likely (Figureattributable 6A,B) to is the likely A6 highway.attributable An to explanation the A6 highway. for mid-afternoon An explanation minimum for mid-afternoon pollution levels minimum is found pollutionwhen examining levels is diurnal found windwhen speedexamining patterns. diur Windnal wind speed speed and CO/NOpatterns.x amountsWind speed are anticorrelated.and CO/NOx amountsDuring the are mid-afternoon, anticorrelated. turbulence During the and mid-afternoon, local wind speed turbulence are at maximum and local (Figure wind3A). speed This leads are toat maximuma deep boundary (Figure layer3A). This and henceleads to more a deep pollutant boundary dilution. layer and hence more pollutant dilution.

1750

Olympic Drive 1500

1250

1000 Silverwater Road

750

500

Total Vehicle Traffic Count (Northbound) Count Traffic Vehicle Total 250

0 6 12 18 24 Hour (AEST)

FigureFigure 5. Hourly meanmeantraffic traffic counts counts (26 (26 May May 2016–13 2016–13 September September 2017) 2017) for Olympic for Olympic Drive Drive (blue circles)(blue circles)and Silverwater and Silverwater Road (red Road diamonds). (red diamonds).

High pollutant mole fractions at low wind speeds for CO and NO in Figure6 indicate local High pollutant mole fractions at low wind speeds for CO and NOxx in Figure 6 indicate local pollutantpollutant sources, sources, because because during during periods periods of of very very low low wind wind speed speed pollutant pollutant transport transport is is supressed. supressed. HighHigh pollution pollution levels levels during during low low wind wind speeds speeds also also suggest suggest accumulations accumulations in in periods periods of of atmospheric atmospheric stability.stability. In In addition addition to to local local traffic traffic and and domestic domestic emissions emissions mentioned, mentioned, there there are are industrial industrial facilities facilities proximate to the Auburn site contributing to the observed CO and NO levels, as documented in proximate to the Auburn site contributing to the observed CO and NOx levels, as documented in Australia’sAustralia’s National National Pollutant Pollutant Inventory. Inventory. Five-hundr Five-hundreded metres metres to to the the NE NE of of the the Auburn Auburn balcony balcony is is a a printery, emitting 2.8 Tyr−1 CO and 4.2 Tyr−1 NO [47]. Nine-hundred metres to the NE is a major printery, emitting 2.8 Tyr−1 CO and 4.2 Tyr−1 NOx x[47]. Nine-hundred metres to the NE is a major brewery, emitting 31 Tyr−1 CO and 150 Tyr−1 NO [48]. The higher pollution associated with wind brewery, emitting 31 Tyr−1 CO and 150 Tyr−1 NOx x[48]. The higher pollution associated with wind −1 speedsspeeds between between 1 1and and 2 2m m s−1 s fromfrom the theWest West is likely is likely the result the result of katabatic of katabatic drainage drainage associated associated with highlywith highly stable stable conditions conditions and andlow lowatmospheric atmospheric mixing mixing that that traps traps urban urban pollution pollution close close to to the the ground-levelground-level [45,46]. [45,46].

AtmosphereAtmosphere2019 2018, ,10 9, x 181 FOR PEER REVIEW 10 ofof 1819

CO (ppmv) NOx (ppbv)

N B N A 8 8

6 60 0.6 6

4 ws 4 ws 50 0.5

2 2 40 W E W E 0.4 0 0

30

0.3

20

0.2 10

0.1

S S

− − Wind speed (ms 1) Wind speed (ms 1)

O (ppbv) −3 3 PM2.5 (µgm )

C N D N

8 30 8

12 6 6 25

4 ws 4 ws 10

20 2 2 8 W E W E 0 0 15 6

10 4

5 2

S S

− − Wind speed (ms 1) Wind speed (ms 1)

Figure 6. Polar bivariate plots of CO, NOx,O3 and PM2.5 ((A–D), respectively) at the Auburn balcony location. Concentric circles from the origin indicate increasing wind speed, direction is indicated by Figure 6. Polar bivariate plots of CO, NOx, O3 and PM2.5 (A–D, respectively) at the Auburn balcony quadrantlocation. andConcentric warmer circles colours from indicate the origin increasing indicate pollutant increasing concentration. wind speed, direction is indicated by

3.2.4.quadrant Ozone and warmer colours indicate increasing pollutant concentration.

3.2.4.Typical Ozone diurnal cycles of ozone are observed when plotting hourly means across a 24-h period (Figure4E) at the Auburn balcony sites, and at the Chullora, Liverpool and Prospect air quality Typical diurnal cycles of ozone are observed when plotting hourly means across a 24-h period monitoring stations. There is a pre-dawn minimum of less than 10 ppb at all sites growing to a (Figure 4E) at the Auburn balcony sites, and at the Chullora, Liverpool and Prospect air quality mid-afternoon maximum greater than 20 ppb, due to the daytime photochemical production of ozone monitoring stations. There is a pre-dawn minimum of less than 10 ppb at all sites growing to a followed by titration of ozone by NO overnight. The relationship between NO and ozone is evident in mid-afternoon maximum greater than 20 ppb, due to the daytime photochemicalx production of the anticorrelation between the species (correlation coefficient, r = −0.57, number of points, n = 38,869). ozone followed by titration of ozone by NO overnight. The relationship between NOx and ozone is This is also evident when comparing the polar bivariate plot of NO (Figure6B) to that of ozone evident in the anticorrelation between the species (correlation coefficient,x r = −0.57, number of points, (Figure6C), and also in the diurnal cycles of the species (Figure4C,E, respectively). The relationship n = 38,869). This is also evident when comparing the polar bivariate plot of NOx (Figure 6B) to that of between ozone and temperature is also clearly expressed in these measurements (r = 0.63, n = 39,539). ozone (Figure 6C), and also in the diurnal cycles of the species (Figure 4C,E, respectively). The Ozone levels are similar between sites, except during summer when ozone is significantly lower at relationship between ozone and temperature is also clearly expressed in these measurements (r = the Auburn balcony site than at the proximate air quality monitoring stations. However, it must be 0.63, n = 39,539). Ozone levels are similar between sites, except during summer when ozone is noted that a reduced number of ozone measurements were taken during the summer maximum at significantly lower at the Auburn balcony site than at the proximate air quality monitoring stations. the Auburn site. This may contribute to the lowered average concentration. Calibration of the ozone However, it must be noted that a reduced number of ozone measurements were taken during the instrument occurred at 14:00 or 15:00 each day, creating a lack of measurements during the daily ozone summer maximum at the Auburn site. This may contribute to the lowered average concentration. Calibration of the ozone instrument occurred at 14:00 or 15:00 each day, creating a lack of

Atmosphere 2019, 10, 181 11 of 18 peak. This also contributes to the lower concentrations (average mean bias: −24%) reported at the Auburn balcony compared to the other sites.

3.2.5. Annual Cycles of Carbon Monoxide, Oxides of Nitrogen and Ozone

Monthly means of CO and NOx (Figure4B,D, respectively) reveal similar seasonal cycles for these species. Highest pollution levels for both pollutants at all sites are observed in May, June or July. Higher winter mole fractions are attributed to a combination of factors: slower photochemical removal, lower boundary layer mixing heights and additional contributions to CO and NOx from combustion heating. CO and NOx are lower at Prospect than at other sites throughout the year. Again, a dependence on wind speed is evident, with the seasonal cycle of wind speed (Figure3B) anticorrelated with those of CO and NOx (Figure4A,C). Monthly mean ozone mole fractions (Figure4F) also align with the expected seasonal cycle at all sites. A December maximum is observed at all sites, coinciding with the period of peak solar irradiance and high summer temperatures. This agrees with previous studies regarding ozone in the Sydney basin, with the importance of extreme heat and biogenic emissions noted [10,49,50]. The May–June minimum is aligned with less daylight hours and cooler temperatures, giving rise to slower photochemistry and less ozone production. Mean mole fractions throughout the year are similar for the three air quality monitoring stations. Ozone measurements are lower at Auburn throughout the year, with the greatest difference observed in late summer, partly due to the reasons previously stated.

3.3. PM2.5

Plotting hourly mean PM2.5 concentration (Figure7A) reveals, as with other pollutants, a similar diurnal cycle between measurement locations. The four sites follow a similar bimodal trend, where the PM2.5 concentration is at a maximum near 06:00, and again in the evening. The higher concentration of PM2.5 during the evening and into the night is most likely the particulates being trapped within the low nocturnal boundary layer. A likely source of particulate pollution at all sites is local traffic, similar to CO and NOx. The trough present in early afternoon PM2.5 concentration is likely due to the growth of a turbulent boundary layer. Evidence for particulate dilution is provided in maximum wind speed coincident with minimum particle concentrations in the mid-afternoon (Figure3A), and minimums in the morning and evening during high observed concentrations of PM2.5. Auburn shows mean concentrations comparable to the other sites, although the morning peak is later than at the other sites, suggesting a possible influence of local traffic that could be associated with school drop-off times. The mean bias for the Auburn balcony with each site is Chullora −1.29 µgm−3, Liverpool −1.42 µgm−3 and Prospect −0.640 µgm−3. Negative values in each instance show that the Auburn balcony sees slightly lower mean PM2.5 than each permanent site. The polar bivariate plot for Auburn (Figure6D) shows the impact of the nearby A6 motorway when winds are from the east. Secondary particulate formation is driven by regional scale processes within the Sydney basin, since the precursors are dominated by biogenic sources from the surrounding forested regions. For this reason, photochemically driven particle formation processes are not expected to contribute significantly to differences between PM2.5 concentrations at the different sites. Annual trends in PM2.5, examinable by plotting monthly mean concentrations (Figure7B), are also similar between all sites. The most notable exception is a very high March mean at Chullora, which is not present at other sites. This localised increase in monthly mean concentration is attributable to a fire that occurred on 22 February 2017 at a recycling plant less than one kilometre from the AQMS [51]. Reduced February and March concentrations at Auburn may be an artefact of a period of reduced measurements due to technical difficulties. All sites show a winter maximum, likely attributable to combustion heating emissions [33]. A smaller, secondary maximum in December–January is due to more active secondary photochemical particle formation processes (partially temperature and oxidant Atmosphere 2018, 9, x FOR PEER REVIEW 12 of 19 Atmosphere 2019, 10, 181 12 of 18

when comparing the annual cycle of wind speed (Figure 3A) to that of PM2.5 (Figure 7B), with the two annual cycles anticorrelated. driven) [52]. The influence of wind speed on PM2.5 is also clear when comparing the annual cycle of wind speed (Figure3A) to that of PM 2.5 (Figure7B), with the two annual cycles anticorrelated.

A B 12 12

) ) 10 3 3

− 10 −

(µgm (µgm 8 2.5 8 2.5 PM PM

6 6

0 6 12 18 23 JFMAMJJASOND hour month

Figure 7. Hourly (A) and monthly (B) mean PM2.5 concentration at the Auburn balcony site and the three surrounding air quality monitoring station sites; 95% confidence intervals in the mean are shaded. Figure 7. Hourly (A) and monthly (B) mean PM2.5 concentration at the Auburn balcony site and the Diurnalthree surrounding and seasonal air quality cycles monitoring of PM10 were station also sites; plotted. 95% confidence The diurnal intervals cycle in (provided the mean are in the Appendixshaded.A, Figure A3A) is very similar to that of PM 2.5 at all sites. The seasonal cycle (AppendixA, Figure A3B) varies significantly, showing summer maxima at all sites and no winter peak. Similar to PM2.5Diurnal, PM10 andconcentrations seasonal cycles at Auburn of PM are10 were lower also than plotted. those at The all permanent diurnal cycle sites (provided as indicated in bythe − − − meanAppendix, bias (Chullora: Figure A3A)−2.26 isµ verygm 3similar; Liverpool: to that− 3.24of PMµgm2.5 at3 ;all Prospect: sites. The−1.53 seasonalµgm 3cycle). (Appendix, Figure A3B) varies significantly, showing summer maxima at all sites and no winter peak. Similar to 4.PM Discussion—Comparison2.5, PM10 concentrations at of BalconyAuburn are Site lower to Regional than th Backgroundose at all permanent sites as indicated by −3 −3 −3 meanThe bias Auburn (Chullora: balcony −2.26 site µgm demonstrates; Liverpool: similar −3.24 diurnal µgm ; andProspect: seasonal −1.53 cycles µgm to). nearby permanent air quality monitoring stations sites for all analysed variables. This implies that similar mechanisms are driving4. Discussion—Comparison variability in pollutant concentrationsof Balcony Site observed to Regional at the Background balcony site and at regional background sites. ThereThe Auburn is some balcony difference site in demonstrates pollution levels similar (amplitude diurnal ofand diurnal seasonal and cycles seasonal to nearby cycles) permanent between sites.air quality Auburn monitoring recorded lowerstations wind sites speed for all than analysed those recordedvariables. at This the implies air quality that monitoring similar mechanisms stations andare slightlydriving higher variability temperatures. in pollutant Higher concentrations levels of carbon observed monoxide at the were balcony observed site at Auburnand at regional that at anybackground of the other sites. three There sites. is some difference in pollution levels (amplitude of diurnal and seasonal cycles)Diurnal between and seasonalsites. Auburn cycles recorded of the pollutants lower wind of most speed concern, than ozonethose andrecorded PM2.5 at, were the similarair quality at themonitoring balcony site stations and at and the otherslightly air qualityhigher monitoringtemperatures. stations. Higher Interestingly, levels of carbon lower levelsmonoxide of O3 andwere PMobserved2.5 were at observed Auburn at that Auburn at any compared of the other to otherthree sites.sites. This reflects previous research in urban areas in theDiurnal case of PM and2.5 seasonalthat showed cycles a of decrease the pollutants in concentration of most concern, with height ozone above and ground-levelPM2.5, were similar [21,22 ].at Thisthe balcony finding providessite and at a the rare other air qualityair quality benefit monitoring to increased stations. urbanisation Interestingly, and lower higher levels population of O3 and densitiesPM2.5 were in Australianobserved at cities, Auburn at least compared for residents to other of highsites. levelThis apartments.reflects previous The research significance in urban and causesareas ofin thethe lowercase of O 3PMamounts2.5 that showed measured a decrease at the balcony in concentration site are less with clear. height Whilst above missing ground-level data may contribute[21,22]. This to the finding lower moleprovides fractions a rare observed, air quality the lowbenefit bias isto consistentincreased throughurbanisation much and of the higher day andpopulation all of the densities year. Titration in Australian by NOx cannotcities, explainat least the for differences residents inof Ohigh3 since level the NOapartments.x values areThe consistentsignificance with and those causes measured of the lower at the O other3 amounts sites. measured However, at despite the balcon a seeminglyy site are significantless clear. Whilst bias, outsidemissing of data the summermay contribute months to the the difference lower mole is typically fractions less observed, than 2 ppb, the low which bias is is within consistent the range through of much of the day and all of the year. Titration by NOx cannot explain the differences in O3 since the

Atmosphere 2019, 10, 181 13 of 18 calibration accuracy of the method. An inverse relationship with wind speed confirms the importance of atmospheric stability on local air pollutant concentrations as noted by Chambers et al. [46]. Some variability is expected between sites as the pollutants measured are highly variable over small spatial scales. The permanent monitoring stations aim to measure regional background levels of pollution; however, the measurements at each site do reflect local sources, with Chullora and Liverpool showing higher levels of pollution than Prospect. Differences between the permanent air quality monitoring stations are greater in all cases than differences between the Auburn balcony site and the air quality monitoring stations. Therefore, we conclude that the regional air quality monitoring stations provide a good representation of pollutant concentrations at the Auburn balcony site, including for the pollutants of most concern in Sydney.

5. Summary and Conclusions The WASPPS-Auburn campaign provided evidence that the diurnal and seasonal cycles of all pollutants at the balcony site were similar to those at the permanent air quality monitoring sites, suggesting common pollutant sources and mechanisms. Traffic signals and the influence of wind speed (as a proxy for surface turbulence and atmospheric stability) dominate diurnal cycles of CO, NOx and PM2.5. Low winter boundary layer heights and the influence of combustion heating provide these species with a winter peak. Ozone follows the opposite trend to NOx with a photochemically driven summer mid-afternoon peak. During the 16-month campaign, differences in pollution levels between the sites were within the expected range, given the high spatial variability of air quality. CO was highest at the Auburn balcony site, but nitrogen oxides were within the range measured at the other sites and the pollutants of most concern (O3 and PM2.5) were lowest at Auburn. Therefore, we conclude that the existing air quality network provides a good representation of typical pollution levels at the Auburn “balcony” site selected for this study. Although this result cannot be generalised to all suburban balconies in Sydney, it demonstrates the effectiveness of the regional air quality monitoring network in western Sydney at providing an indication of personal exposure to outdoor air quality pollutants at a simulated balcony site.

Author Contributions: Conceptualization, C.P.-W.; Methodology, C.P.-W., G.G. and J.K.; Validation, G.G. and J.K.; Formal Analysis, J.B.S., C.P.-W., É.-A.G., S.B. and J.G.; Investigation, F.P., T.N., D.D. and H.F.; Writing—Original Manuscript, J.B.S., C.P.-W., J.G. and T.K.; Writing—Review and Editing, C.P.-W., and F.P.; Supervision, C.P.-W. and É.-A.G.; Project Administration, C.P.-W.; Funding Acquisition, C.P.-W. Funding: This research was funded by Australia’s National Environmental Science Program through the Clean Air and Urban Landscapes hub. Acknowledgments: With thanks to all the staff of the NSW Office of Environment and Heritage and EPA, who contributed to the provision of publicly available air quality data in western Sydney. Thanks are also due to Paul Naylor and Douglas Greening of the NSW Master Plumbers Association for their willingness to provide the suburban “balcony” site and their help with the ongoing operation of the instruments. Conflicts of Interest: The authors declare no conflicts of interest. Atmosphere 2019, 10, 181 14 of 18

Atmosphere 2018, 9, x FOR PEER REVIEW 14 of 19 Appendix A

00:00−06:00 06:00−12:00 00:00−06:00 06:00−12:00 0% 0% N N 30% N 30% N 40% 40% 30% 30% 20% 20% 20% 20% 10% 10% 10% 10% W E W E W E W E

S S S S 12:00−18:00 18:00−24:00 12:00−18:00 18:00−24:00 0% 0% N N 30% N 30% N 40% 40% 30% 30% 20% 20% 20% 20% 10% 10% 10% 10% W E W E W E W E

S S S S

0 to 2 2 to 4 4 to 6 6 to 7.64 0 to 2 2 to 4 4 to 6 6 to 12.8 Auburn Chullora − − (m s 1) (m s 1)

00:00−06:00 06:00−12:00 % 00:00−06:00 % 06:00−12:00 40% N 40% N N N 30% 30% 20% 20% 20% 20% 10% 10% 10% 10% W E W E W E W E

S S S S 12:00−18:00 18:00−24:00 % 12:00−18:00 % 18:00−24:00 40% N 40% N N N 30% 30% 20% 20% 20% 20% 10% 10% 10% 10% W E W E W E W E

S S S S

0 to 2 2 to 4 4 to 6 6 to 10.1 0 to 2 2 to 4 4 to 6 6 to 9.5 Liverpool Prospect − − (m s 1) (m s 1)

Figure A1. Site-specific wind roses divided by time of day. Measurements were binned into four Figure A1. Site-specific wind roses divided by time of day. Measurements were binned into four periods: 00:00–06:00, 06:00–12:00, 12:00–18:00 and 18:00–00:00. Colour represents wind speed, while periods: 00:00–06:00, 06:00–12:00, 12:00–18:00 and 18:00–00:00. Colour represents wind speed, while distance from the origin represents the proportion of total wind direction measurements present in distance from the origin represents the proportion of total wind direction measurements present in each 30◦ segment. each 30° segment.

Atmosphere 2019, 10, 181 15 of 18 Atmosphere 2018, 9, x FOR PEER REVIEW 15 of 19

spring (SON) summer (DJF) spring (SON) summer (DJF) 50% N 50% N 30% N 30% N 40% 40% 30% 30% 20% 20% 20% 20% 10% 10% 10% 10% W E W E W E W E

S S S S autumn (MAM) winter (JJA) autumn (MAM) winter (JJA) 50% N 50% N 30% N 30% N 40% 40% 30% 30% 20% 20% 20% 20% 10% 10% 10% 10% W E W E W E W E

S S S S

0 to 2 2 to 4 4 to 6 6 to 7.64 0 to 2 2 to 4 4 to 6 6 to 12.8 Auburn Chullora − − (m s 1) (m s 1)

spring (SON) summer (DJF) spring (SON) summer (DJF) 0% 0% 40% N 40% N N N 30% 30% 20% 20% 20% 20% 10% 10% 10% 10% W E W E W E W E

S S S S autumn (MAM) winter (JJA) autumn (MAM) winter (JJA) 0% 0% 40% N 40% N N N 30% 30% 20% 20% 20% 20% 10% 10% 10% 10% W E W E W E W E

S S S S

0 to 2 2 to 4 4 to 6 6 to 10.1 0 to 2 2 to 4 4 to 6 6 to 9.5 Liverpool Prospect − − (m s 1) (m s 1)

Figure A2. Site-specific wind roses binned by season. Colour represents wind speed, while distance Figure A2. Site-specific wind roses binned by season. Colour represents wind speed, while distance from the origin represents the proportion of total wind direction measurements captured within each from the origin represents the proportion of total wind direction measurements captured within each 30◦ segment. 30° segment.

Atmosphere 2018, 9, x FOR PEER REVIEW 16 of 19 Atmosphere 2019, 10, 181 16 of 18

26 A 25 B 24

) ) 22 3 3 − − 20 20 (µgm (µgm 10 10 18 PM PM

16 15

14

0 6 12 18 23 JFMAMJJASOND hour month

FigureFigure . A3.Hourly Hourly (A ()A and) and monthly monthly (B) mean(B) mean PM10 PMconcentration10 concentration at the at Auburn the Auburn balcony balcony site and site three and surroundingthree surrounding air quality air monitoringquality monitoring station sites; station 95% sites; confidence 95% confidence intervals in intervals the mean in are the shaded. mean are shaded. References

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