7.4 A CLIMATOLOGY OF PHOTOCHEMICAL SMOG EPISODES IN SYDNEY AUSTRALIA

Melissa Hart*, Richard de Dear and Robert Hyde Department of Physical Geography, Macquarie University, NSW, Australia

In 1998, the Australian National 1. INTRODUCTION Environment Protection Council (NEPC) Concentrations of ozone often exceed produced a National Environment Protection Australian air quality goals in Sydney during Measure for Air Quality (the Air NEPM) summer. The meteorological conditions (NEPC, 1998). The Air NEPM provided for associated with photochemical smog in the the first time in Australia a set of national Sydney region and surrounds are complex. ambient air quality standards. The Air Photochemical smog episodes are generally NEPM standards for ozone are 100 ppb for confined to the months October to March, a 1-hour average concentration and 80 ppb inclusive. Sydney is located on the eastern for a 4-hour average, with an allowable coast of Australia at latitude -33.8ºS (Figure exceedance of 1 day per year. Furthermore 1), and experiences a temperate climate the New South Wales (NSW) state with warm to hot summers and cool to cold environmental regulatory body the winters (BoM, 1991). The main urban areas Department of Environment and are located within a basin bound by Conservation (DEC) has set long-term goals elevated terrain to the north, west and south for NSW based on The World Health (Figure 2). The weather in the region is Organization (WHO) ozone goals of 80 ppb affected by relatively complex topography (1-hour average) and 60 ppb (4-hour with overnight cold-air drainage flows, average). Figure 3 presents a graph particularly during cooler months and showing the number of days in which the Air frequent sea breezes during the warmer NEPM ozone goal of 100 ppb was months. exceeded over the 10-year period 1992 to 2001. Days in which the exceedance can be attributed to bushfires within Sydney and surrounding regions are presented in purple.

NT QLD WA

SA

NSW Sydney Vic

Tas Scale: 1:2 500 000 © copyright Commonwealth of Australia (Geoscience Australia), 2004 Modified from :http:// www.ga.gov.au/map/ 0 20 Figure 1 Location map of Sydney, (-33.8º S) kilometres ______Figure 2 Topography of Sydney and surrounding * Corresponding author address: Melissa Hart, region and location of NSW DEC air monitoring sites Dept. of Physical Geography, Macquarie University, NSW, 2109, Australia. +61 (0)2 9850 9612 e-mail: [email protected] Number of Days the air NEPM for 1-hour ozone is exceeded 30

25 Exceedances of the ozone goal attributed to bushfired

Days in which the ozone goal is exceeded 20

15 Days

10

5

0 Jan - Mar Oct 1992 - Oct 1993 - Oct 1994 - Oct 1995 - Oct 1996 - Oct 1997 - Oct 1998 - Oct 1999 - Oct 2000 - Oct - Dec 1992 Mar 1993 Mar 1994 Mar 1995 Mar 1996 Mar 1997 Mar 1998 Mar 1999 Mar 2000 Mar 2001 2001

Figure 3 Number of days in which the Air NEPM ozone goal of 100 ppb was exceeded Previous studies of photochemical smog This climatology has been produced using formation in Sydney are often episode- multivariate statistical techniques including based and there remain features in the principal component analysis and cluster occurrence of photochemical smog that are analysis in order to assign days into yet to be fully explained (Hyde, et al. 1995). meteorologically homogeneous synoptic A study by Leighton and Spark (1995) categories. Meteorological inputs to these produced a manual classification of mean statistical procedures include both surface sea level synoptic maps to ascertain the and upper air observations, for warm relationship between synoptic climatology months (October to March) over a ten year and pollution events in Sydney. They period (1992 – 2001). identified the main synoptic situations Days in which Sydney’s air quality may covering the eastern Australian region for have been affected by bushfires were winter and summer associated with removed from analyses. Systematic records moderate to high pollution events. The of bushfire activity in Sydney are scarce. amount of time an anticyclone remained in The most comprehensive data came from the region was also related to number of the National Parks and Wildlife Service pollution days. They found summertime (NPWS) wildfire database, which covers pollution events to be associated with a light wildfire activity from 1995 to the present. west to northwesterly gradient wind. Using this database, days in which there Meso-scale conditions have a large was significant bushfire activity in the influence on the formation of photochemical Sydney region were isolated and daily smog in the Sydney basin. High ozone maximum observations of ozone and PM10 peaks, particularly in the central and were then compared for both bushfire days western regions of Sydney, are most and non-bushfire days. Days in which there commonly associated with an afternoon sea were bushfires in the Sydney region breeze that transports precursor emissions generally showed a marked increase in across the Sydney basin. particulate concentrations compared to non- In order to gain a better understanding bushfire days. From this analysis, days in of the synoptic signatures behind which daily maximum values of ozone photochemical smog processes, this paper exceeded 80 ppb and PM10 exceed 110 presents an objective synoptic climatology µg/m3 were deemed days in which air of photochemical smog episodes in Sydney. quality in Sydney was probably being affected by bushfires. A threshold of 80 ppb as much of the residual variance as possible ozone was chosen as it corresponds to the while remaining orthogonal (i.e. completely NSW DEC long-term 1-hour ozone goal. independent) to the first in data-space. Twenty-seven days were identified between Remaining components explain less 1992-2001 using these criteria; these days variance than the proceeding components. were removed from the analyses. By retaining only a proportion of the On a number of days in which there principal components, a large amount of the were bushfires in the Sydney region ozone original variance can be explained whilst and particulate concentrations were below substantially reducing the size of the data the criteria described above. However, on matrix. some occasions synoptic, regional and Each principal component comprises a meso-scale winds may have transported series of loadings that represent the some residual bushfire air into the Sydney correlation between the principal component Basin; however the resultant impact on and the meteorological parameter. The subsequent ozone concentrations was low. larger the component loading the more Therefore, these days were not excluded important the meteorological parameter is in from the synoptic classification. the interpretation of that principal component. Once the principal components 2. SYNOPTIC CLIMATOLOGY METHODS and their respective loadings are A synoptic climatology of photochemical established it is necessary to ascertain the smog episodes in Sydney was undertaken. relationships between the original raw This analysis involved using multivariate variables for each day and the principal statistical techniques including principal components. This is achieved through the component analysis and a two-stage cluster calculation of component scores for each analysis to classify days into day, which are values for each day’s meteorologically homogenous synoptic weather observations based on the principal categories. These synoptic categories were components (PC). Thus, days with similar then related to ground level ozone meteorology conditions will exhibit concentrations. The method of synoptic proximate principal component scores classification used in this research is the (Shahgedanova, et al. 1998). circulation-to-environment approach, in To generate synoptic categories PCA which the classification is produced first and was used in conjunction with cluster is then related to the environmental variable analysis. Clustering procedures were used in question (Yarnal 1993). This method is to group days with similar component becoming more frequent in air pollution scores and to assign each day into a climatology studies, particularly in the study meteorologically homogeneous subset of of photochemical smog (e.g. Cheng, et al. the data (Kalkstein and Corrigan, 1986; 1992; Eder, et al. 1994; Davis, et al. 1998; Shahgedanova, et al. 1998; Greene, et al. Greene, et al. 1999; Schreiber, 2000). 1999). The component scores matrix The multivariate statistical techniques (number of days times the retained PCs) were used to group suites of meteorological obtained from PCA served as the input variables into synoptic categories found to matrix for cluster analysis. The reduced size be representative of the air mass and the absence of co-linearity make it ideal characteristics at that time. Principal data for clustering (Davis, et al. 1998). Component Analysis (PCA) was used as a A two-stage clustering technique was data reduction technique. Data reduction is used. Firstly, average-linkage, a achieved by finding linear combinations hierarchical, agglomerative method was (principal components) of the original used to determine the number of clusters variables, which account for as much of the and the mean conditions within each cluster. total variance in the original variables as These initial clusters were then used as possible (Statheropoulos, et al. 1998). The input in to k-means clustering, a non- components are ordered such that the first hierarchical iterative method. component explains the greatest proportion As each of the clusters exhibits a of the variance and the second accounts for distinctive air mass and synoptic signature, a characteristic regime of pollution concentration should be associated with where ozone concentrations are largely each because of the critical impact of governed by the transport of precursors weather conditions on the dispersion or over a stream of continuous urban and accumulation of air pollutants (Cheng, et al. industrial centres. Whilst there are emission 1992). sources in the surrounding region, which may transport emission towards Sydney in 2.1 Selection of meteorological variables regional flows, Sydney is relatively isolated Surface and upper air meteorological from other large urban centres, therefore data for warm months (Oct-Mar) over a ten boundary layer flows tend to be clean and year period (1992 – 2001) were used as only contain background concentrations of input into the statistical analysis. The ozone. general goal of any synoptic climatological Sydney’s environment is geographically method is to combine individual weather complex, there are controls on weather elements into groups or classes that are patterns from the surrounding topography, representative of the synoptic scale situation and the location of the Sydney basin with at a moment in time. Therefore a coherent topography to three sides and the sea to the combination of meteorological elements is east generates a complicated drainage flow, required that is representative of distinct air sea breeze circulation. Therefore, it was mass types. decided that the inclusion of upper air Previous applications of this synoptic variables was imperative in gaining a climatology technique in air pollution studies comprehensive understanding of the air have concentrated on surface mass characteristics behind photochemical meteorological variables as inputs to the smog episodes in Sydney. In order to find statistics. For example, (Kalkstein and the most appropriate suite of meteorological Corrigan, 1986) recommend the use of variables for use in the synoptic surface variables, assuming that the relative classification a series of experiments were meteorological homogeneity of an air mass undertaken using different suites of in its horizontal extent allows inferences variables. Table 1 shows all meteorological concerning vertical processes and variables used in the analyses with the associated atmospheric stability. However, variables used for each configuration some studies have included upper air marked. observations such as twice daily Configuration 1 included only surface measurements of upper air temperature, variables collected from the Australian dew point temperature, and u and v wind Bureau of Meteorology’s Sydney Airport components (Eder, et al. 1994; Davis, et al. Automatic Weather Station (AWS), which is 1998). a coastal site. Surface variables included: The common meteorological variables used in this type of PCA include: dry bulb * 6am and 3pm dry bulb and dew point temperature, dew point temperature or temperatures (defining the thermal and relative humidity, mean sea level pressure, moisture properties of the air mass) total cloud cover or global solar radiation * 6am and 3pm pressure and u and v wind components. Other * 6am and 3pm total cloud cover investigations have included visibility (representing incoming solar radiation) (Kalkstein and Corrigan, 1986), vapour * 6am and 3pm u and v wind components pressure (McGregor and Bamzelis, 1995), (indicative of surface flow patterns, and total daily solar insolation and morning and important to the transport and dispersion afternoon mixing heights (Eder, et al. 1994; of pollutants). Davis, et al. 1998). Studies by (Eder, et al. 1994) and (Davis, et al. 1998) on Birmingham, Alabama and Houston, Texas respectively have also included upper air temperature and wind parameters from 850 hPa. Many of the studies mentioned previously are in areas of the United States Table 1 A summary of the different configurations of meteorological variables used for input to Principal Components Analysis

Meteorological variables used as input to PCA

Configuration Configuration Configuration Meteorological Variables 1 2 3 Surface Data Temperature (°C) v v v Dew point (°C) v v v u wind (m/s) v v v v wind (m/s) v v v

6:00 AM MSLP (hPa) v v v total cloud cover (oktas) v v v Temperature (°C) v v v Dew point (°C) v v v u wind (m/s) v v v v wind (m/s) v v v

3:00 PM MSLP (hPa) v v v total cloud cover (oktas) v v v Upper Air Data 850 hPa temperature (°C) (~1500 m) v v

850 hPa dew point temperature (°C) v v 6:00 AM Mixing height (m) v v 850 hPa temperature (°C) v v 850 hPa dew point temperature (°C) v v 850 hPa u wind (m/s) v v 850 hPa v wind (m/s) v v 3:00 PM 975 hPa temperature (°C) (within sea breeze) v 925 hPa temperature (°C) (above sea breeze) v

Configuration 2 included the same understanding the depth of the sea breeze. surface variables as above, as well as a The occurrence and nature of the sea collection of upper air variables: breeze in Sydney during summer has an * 6am and 3pm 850 hPa dry bulb and dew important influence on ozone point temperatures concentrations, particularly in western * 3pm 850hPa u and v wind components Sydney. * 3pm mixing height. Configuration 3 included the surface and Upper air observations were obtained from upper air variables above plus an additional the Australian Bureau of Meteorology’s two extra upper air variables: twice daily radio-sonde ascent at Sydney * 3pm 975 hPa temperature Airport. Observations from the 850hPa level * 3pm 925 hPa temperature were chosen as it is a commonly measured These variables were chosen as the level and the air mass at this level is above temperature at 975 hPa is often indicative of the planetary boundary layer. the temperature within the sea breeze and Mixing height was included because of the 925 hPa temperature is indicative of the its importance in the dispersion and dilution conditions just above the sea breeze. These of pollutants. Mixing height was derived variables were included in order to study the graphically from upper air temperature influence of the sea breeze on air mass traces as the point at which a parcel of air conditions associated with photochemical rising dry adiabatically crosses the smog episodes. environmental lapse rate (Holzworth, 1967). Observations taken at 6am and 3pm Mixing height was derived from the 3pm were used in the statistical analysis as they temperature trace which is important in are times close to minimum and maximum temperatures and are commonly measured 3. SYNOPTIC CLIMATOLOGY RESULTS times for the recording of surface USING METEOROLOGICAL VARIABLES meteorological observations. These times SPECIFIED IN CONFIGURATION 3 also coincide with the twice daily radio- Eleven synoptic categories were found sonde ascents. in Sydney during the warm season. Each configuration of variables was Meteorological inputs from both surface and analysed using the above mentioned upper air observations from Sydney airport statistical procedures, ozone concentrations were used in the development of the within each synoptic category were then synoptic climatology and ozone analysed. Configurations were compared by concentrations associated with each of the evaluating the maximum ozone synoptic categories have been investigated. concentrations observed in each of the One synoptic category was found to be synoptic categories. associated with high pollution Nine, ten and eleven synoptic categories concentrations. Of the days in the high were found for configurations 1, 2 and 3, ozone cluster, 48% were found to exceed respectively. Table 2 shows the ozone the New South Wales proposed 1-hour concentrations associated with each of the ozone goal (80 ppb), a further 32% were synoptic categories for each configuration. found to experience ozone concentrations Configuration 1, containing surface between 60 to 80 ppb, while the remaining variables only, produced nine warm season 20% of days recorded concentrations less synoptic categories for Sydney, one of these than 60 ppb ozone. On the basis of an categories (cluster 2) contained 55% of all examination of surface synoptic charts, high pollution days (daily maximum ozone enhanced ozone concentrations were found greater than 80 ppb), however only 20% of to be associated with a high pressure the 414 days falling within this category system located in the middle to eastern exceeded this criteria. Configuration 2 Tasman Sea producing light north westerly improves the isolation of high pollution days gradient winds, high afternoon with 68% of all high pollution days falling temperatures, the presence of an afternoon within the synoptic category containing the sea breeze, a shallow mixing height and highest mean maximum daily ozone warming aloft. Table 3 presents the mean concentrations; 31% of the 293 days within meteorological conditions associated with this category are greater than 80 ppb. the synoptic category associated with Configuration 3 also had 68% of all high highest ozone concentrations. pollution days falling within the synoptic To further understand the category associated with highest ozone meteorological processes operating during concentration. However, with the inclusion Sydney’s pollution episodes, a selection of of extra upper temperature variables in days falling in this high pollution synoptic order to define the upper temperature category were analysed in greater detail, profile, particularly with regard to processes particularly the meteorological differences within and above the sea breeze, some of between days with similar synoptic the low pollution days falling within the high conditions, yet quite different ozone pollution category in Configuration 2 have concentrations. The ozone season from been reassigned to other synoptic situations October 2000 to March 2001 was chosen to in Configuration 3. The daily maximum analyse in greater detail. This season was ozone concentration associated with the chosen as it represented a relatively severe high pollution category has been increased ozone season with seventeen exceedances in configuration 3 and 48% of all days within of the current ozone goal being recorded; in this category experienced daily maximum addition the season experienced relatively ozone concentrations greater than 80 ppb. small influences from bushfire activity, with This has confirmed that the suite of only two of the exceedances being meteorological variables used in attributed to bushfires. configuration 3 were the best at isolating the . air mass characteristics behind photochemical smog episodes for Sydney. 9 1 44 6% 1% 0% 11 (156) 0 0 6 31 52 20 0% 0% 0% 6% 4% 21% 10 (5) 10 (95) 0 0 53 82 28 58 34 26 31 8% 0% 0% 0% 22% 19% 23% 17% 19% 9 (5) 9 (372) 9 (149) 0 0 4 0 1 31 48 44 14 0% 0% 0% 0% 0% 9% 1% 0% 14% 8 (38) 8 (29) 8 (149) 0 0 9 1 0 28 52 40 30 0% 0% 0% 5% 7% 2% 0% 0% 20% 7 (34) 7 (46) 7 (198) 0 0 5 3 0 35 38 24 47 0% 0% 0% 2% 4% 0% 0% 10% 11% 6 (80) 6 (28) 6 (247) 9 3 4 1 47 30 49 0.0 0.0 4% 2% 0% 0% 0% 4% 0% 13% 15% 5 (70) 5 (44) 5 (26) 0 0 6 1 1 0 29 50 30 0% 0% 0% 3% 0% 0% 0% 0% 16% 4 (38) 4 (158) 4 (200) 3 59 47 35 45 20 61 83 30 2% 2% 24% 18% 24% 12% 34% 12% 22% 3 (192) 3 (167) 3 (241) 60 90 81 74 88 92 87 61 92 22% 20% 55% 30% 31% 68% 32% 48% 68% 2 (414) 2 (293) 2 (193) 0 0 5 0 5 30 31 38 26 0% 0% 0% 2% 0% 0% 9% 2% 4% 1 (283) 1 (252) 1 (283)

9 10 11 Cluster Number (n) Cluster Number (n) Cluster Number (n) 80 ppb) falling in cluster 80 ppb) falling in cluster 80 ppb) falling in cluster < 80 ppb < 80 ppb < 80 ppb 3 3 3 = = =

3 3 3 O O O < 80 ppb < 80 ppb < 80 ppb = = = 3 3 3 80 ppb 80 ppb 80 ppb O O O ssociated with each configuration ======80 ppb 80 ppb 80 ppb = = =

3 3 3 Comparison of maximum ozone concentrations for different synoptic categories- configuration 1,2 and 3 Ozone concentration a 2 Table Configuration 1 Configuration 2 Configuration 3 Number of clusters Mean daily ozone concentration (ppb) for cluster Number of days maximum 60 ppb Percentage of days maximum 60 ppb Number of days maximum O Percentage of days maximum O3 Percentage of all high pollution days (O Number of clusters Mean daily ozone concentration (ppb) for cluster Number of days maximum 60 ppb Percentage of days maximum 60 ppb Number of days maximum O Percentage of days maximum O3 Percentage of all high pollution days (O Number of clusters Mean daily ozone concentration (ppb) for cluster Number of days maximum 60 ppb Percentage of days maximum 60 ppb Number of days maximum O Percentage of days maximum O3 Percentage of all high pollution days (O Table 3 Mean meteorological conditions associated with the high pollution category

Meteorological Cluster Number (number of days in cluster) Variables 1 (283) 2 (193) 3 (241) 4 (200) 5 (26) 6 (28) 7 (46) 8 (149) 9 (5) 10 (95) 11 (156) Temperature (°C) 20.3 21.2 17.8 17.3 19.5 18.6 15.1 17.0 19.8 20.4 13.3 Dew Point (°C) 17.8 18.5 14.8 13.1 15.8 11.8 7.7 13.2 6.7 17.2 8.1 u Wind (m/s) -2.5 1.0 0.5 -3.9 1.9 1.5 0.9 0.9 3.4 1.2 -0.8 v Wind (m/s) 0.9 -0.1 -0.7 0.9 -0.6 -1.4 -2.9 -0.4 -4.7 -0.4 -2.3 Surface Pressure (hPa) 1015 1012 1018 1020 1008 1008 1007 1015 995 1008 1019 6am Cloud Cover (oktas) 6.3 3.5 2.4 6.0 5.5 2.2 3.7 5.3 5.4 5.9 2.7 850hPa Temperature 12.4 18.1 12.2 6.8 15.9 14.1 7.2 9.6 10.7 15.9 5.3 (°C) 850hPa Dew Point (°C) 8.6 4.9 0.2 4.3 4.4 -2.6 -0.7 3.4 0.3 6.2 -2.5 Upper Air Temperature (°C) 23.2 29.2 25.6 20.4 31.9 32.1 23.1 22.6 24.5 25.5 19.8 Dew Point (°C) 17.4 18.2 14.4 12.7 11.8 3.6 3.0 13.6 4.3 17.2 9.1 u Wind (m/s) -2.6 4.3 3.2 -3.9 3.4 2.5 -0.9 4.0 1.6 2.1 -1.5 v Wind (m/s) 3.3 4.8 5.0 3.3 -5.4 -6.2 -6.7 4.5 -12.3 2.0 4.3 Surface Pressure (hPa) 1015 1010 1016 1020 1004 1004 1006 1012 996 1006 1018 Cloud Cover (oktas) 6.1 2.9 1.9 5.9 5.2 2.4 3.5 5.1 6.2 6.0 2.7 Mixing Height 551 331 646 878 1680 2698 1977 562 1709 290 800

3pm (m) 850hPa Temperature 12.6 20.0 14.7 7.5 16.9 16.5 8.1 11.9 10.5 16.3 7.6 (°C) 850hPa Dew Point (°C) 8.2 5.8 -0.9 3.9 6.4 0.0 -1.8 4.2 0.1 7.3 -3.6 850hPa

Upper Air u Wind (m/s) -0.8 1.1 -0.3 -2.2 3.4 2.9 -0.6 3.5 5.7 4.1 -1.1

850hPa v Wind (m/s) -0.6 -4.8 -2.9 0.4 -10.7 -9.3 -10.8 -6.0 -23.9 -10.5 -5.1 Daily Maximum Ozone (ppb) 38 87 61 30 49 47 30 44 31 52 44

3.1 A case study of two days falling * The 6am, 10am, 3pm and 10pm (EST) within the high pollution category radio-sonde ascents made at Sydney The 2000-2001 photochemical smog Airport season has been examined in greater detail * Wind profiles at Sydney Airport for 6am in order to examine the synoptic and meso- and 10am (EST). scale features leading to high pollution On each day the overall surface events in Sydney. To illustrate the synoptic situations were characteristic of complexity of both synoptic and meso-scale features observed during most ozone wind flows, and the vertical temperature events in Sydney (Hyde, et al. 1995), with a structure, on days predicted to be high region of high pressure in the Tasman Sea photochemical smog in Sydney, two days and a ridge extending north east across falling within the high pollution category northern New South Wales (NSW) and were examined in more detail: Queensland (QLD). On both days low-level * 21 December 2000 - experienced a 6am vertical temperature profiles show a maximum hourly average ozone shallow mixed layer at the surface and a concentration of 158 ppb; sharp capping inversion above. However, * 22 December 2000 – fell within the high on the 21st of December the surface winds pollution category, however maximum in the morning were southeasterly, whereas nd hourly average ozone concentrations in on 22 of December the surface winds Sydney reached only 62 ppb. were north-northeast to northerly. Below we A selection of the available meteorological discuss features of the surface winds, and data for each day is shown in upper wind and temperature structures that Figure 4 and Figure 5 respectively. For each probably resulted in these two events event the following data are presented: having quite different maximum hourly * The surface synoptic chart at 10am and average ozone concentrations in Sydney. 10pm Eastern Standard Time (EST) * Half-hourly surface winds at Sydney Airport (Mascot) at the coast 21st December 2000 Daily maximum O3 = 158 ppb

BoM Analysis Chart BoM Analysis Chart 10am 10pm

Mascot Temperature 16 360 3500 6am T 14 315 3000 3pm T 12 270 2500 6am Td 10 225 3pm Td 8 180 2000 DALR 6 135 (degrees) 1500

4 90 Wind Direction

Height (m) 1000 Wind Speed (m/s) 2 45 500 0 0 0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00 0 Time Wind Speed Wind Direction -20 0 20 40 Half hourly surface winds – Sydney Airport Temperature (°C) Twice daily air-sonde ascent – Sydney Airport Wind Direction (degrees) 10am Wind Direction (degrees) 3pm Wind Direction (degrees) Wind Direction (degrees) 6am 0 45 90 135 180 225 270 315 360 0 45 90 135 180 225 270 315 360 0 45 90 135 180 225 270 315 360 10pm 0 45 90 135 180 225 270 315 360 5000 4500 5000 4500

WS WS WS WS 4500 4000 4500 4000 WD WD WD WD 4000 4000 3500 3500

3500 3500 3000 3000 3000 3000 2500 2500 Height (m) Height (m) Height (m) 2500 Height (m) 2500 2000 2000 2000 2000 1500 1500 1500 1500 1000 1000 1000 1000

500 500 500 500

0 0 0 0 0 5 10 15 20 25 30 0 5 10 15 20 25 30 0 5 10 15 20 25 30 0 5 10 15 20 25 30 Wind Speed (m/s) Wind Speed (m/s) Wind Speed (m/s) Wind Speed (m/s)

Figure 4 Meteorological conditions associated with a high ozone day, 21st December, 2000

3.1.1 High ozone event – 21st December by an inversion with slightly stable warmer 2000 west-southwesterly flow above. On the basis of the synoptic chart The shallow southerly flow present at presented in Figure 4, surface winds at Sydney Airport during the early hours of the Sydney on the morning of the 21st morning is characteristic of some generic December should be north to north-easterly. ozone events in Sydney (Hawke, et al. However, the surface winds at Sydney 1978). During these events these shallow Airport show a moderate (4-5 m/s) south to flows move into the Sydney Basin late the south-easterly during the morning gradually precious evening or early morning. If this backing late morning and early afternoon to shallow flow, capped by an inversion, is still become an east to northeast sea breeze; present after sunrise then morning the wind then turns north-northeasterly in precursors of photochemical smog are the late afternoon and evening. The 6am trapped and transported across the Sydney radio-sonde profile presented in Figure 4 Basin potentially forming high illustrates that this southeasterly flow is concentrations downwind. In addition, the quite shallow and at around 300m is capped presence of a shallow east to north east sea breeze, as occurred on this day, continues to trap and transport precursor emissions Sydney are complex and include both across the Basin contributing to ongoing synoptic and meso-scale processes. The high concentrations of ozone. synoptic climatology produced in this research includes meteorological variables 3.1.2 Low ozone event – 22nd December that encompass processes from both these 2000 scales. The synoptic climatology has The day after the event discussed above isolated one synoptic situation associated shows a very similar surface synoptic chart, with high pollution episodes. By studying the with a high in the eastern Tasman Sea and synoptic and associated meso-scale a ridge of high pressure extending processes experienced within this category northwest over northern NSW and Qld. it has been possible to ascertain some of However, in contrast to the previous day, the determining factors required to produce where surface winds were initially south to a high pollution day in Sydney. south-easterly, surface winds on the 22nd The two days examined in detail, both December are north-northeasterly having almost identical synoptic charts, alongshore winds throughout the night, illustrate the difficulty in predicting high turning northerly at 6am and continuing in ozone events in Sydney. While on each day this direction until the onset of a the temperature profiles at 6am show a northeasterly sea breeze at around shallow well-mixed layer capped by an 3pm.The morning radio-sonde profile shows inversion, winds within this surface layer are a characteristic temperature profile of this associated with quite different meso-scale st type of day with a very shallow layer within flows. For example, on the 21 December the north-northeasterly alongshore flow there were overnight and morning south to capped by a deep inversion to around 800 south-easterly winds, while on the morning nd metres and an adiabatic layer to of the 22 December winds were approximately 1800 metres. alongshore north-northeasterly before the The 6am wind profile presented in breakdown of the surface layer and onset of Figure 5 is consistent with the overall a moderate to strong northerly synoptic flow. st synoptic situation, with moderate On the 21 of December the north to northwesterly gradient winds above the north-west synoptic flow, combined within surface. The afternoon profile shows a onshore north-east sea breeze, could be northeasterly sea breeze capped by a expected to govern ozone concentrations in shallow inversion and a deep layer of west- Sydney. However, as discussed above it northwesterly winds above. However, the was a south-easterly meso-scale flow that main difference between this day and other most probably produced such high occasions with similar synoptic situations concentrations in Sydney. and north east to north westerly winds, is In contrast, the following day, where the strong winds observed after 9am at synoptic conditions were almost identical Sydney Airport. There was also a rapid and concentrations of ozone were predicted increase in surface temperatures at the to be high, the rapid breakdown of the coast on this day which would have rapidly surface inversion morning and subsequent eroded the inversion observed in the 6am mixing down of moderate to strong northerly radio-sonde ascent. Consequently, following gradient winds resulted in quite low the breakdown of the inversion, moderate to concentrations of ozone. strong northerly winds would have mixed The examples above illustrate the down to the surface and precursor complexity and difficulty of predicting some emissions in the Sydney Basin would have high ozone events in Sydney, and in rapidly diluted and dispersed, with the well particular the influence of different meso- mixed layer extending to 1800m. scale flows, therefore a more detailed analysis of the relative influence of the 4. DISCUSSION AND PLANS FOR current parameters used in the statistic FUTURE RESEARCH analyses is necessary to determine the Meteorological conditions associated relative importance of individual factors on with photochemical smog episodes in individual days.

22nd December 2000 Daily maximum O3 = 62 ppb

BoM Analysis Chart BoM Analysis Chart 10am 10pm

Airport Temperature 16 360 3500

14 315 6am T 3000 3pm T 12 270 2500 6am Td 10 225 3pm Td 8 180 2000 DALR

6 135 (degrees) 1500 Wind Direction

4 90 He ight (m) 1000 Wind Speed (m/s) 2 45

0 0 500 0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00 Time Wind Speed 0 Wind Direction -20 -10 0 10 20 30 40 Temperature (°C) Half hourly surface winds – Sydney Airport Twice daily air-sonde ascent – Sydney Airport

6am Wind Direction (degrees) Wind Direction (degrees) 4pm Wind Direction (degrees) 10pm Wind Direction (degrees) 0 45 90 135 180 225 270 315 360 10am0 45 90 135 180 225 270 315 360 0 45 90 135 180 225 270 315 360 0 45 90 135 180 225 270 315 360 4500 4500 4500 4500

WS WS WS 4000 4000 WS 4000 4000 WD WD WD WD 3500 3500 3500 3500

3000 3000 3000 3000

2500 2500 2500 2500 Height (m) Height (m) Height (m) Height (m) 2000 2000 2000 2000

1500 1500 1500 1500

1000 1000 1000 1000

500 500 500 500

0 0 0 0 0 5 10 15 20 25 30 0 5 10 15 20 25 30 0 5 10 15 20 25 30 0 5 10 15 20 25 30 Wind Speed (m/s) Wind Speed (m/s) Wind Speed (m/s) Wind Speed (m/s) Figure 5 Meteorological conditions associated with a medium ozone day, 22nd December, 2000 In future research it is hoped to refine 10am wind accents may help in the this climatology even further by assessing understanding of synoptic movements the importance of current and additional throughout the morning. variables to the statistical analyses. A This analysis is also to be expanded selection of the additional variables currently through use of the Australian being considered includes maximum Commonwealth Scientific and Industrial temperatures experienced at Richmond, in Research Organisation’s (CSIRO) 3D wind western Sydney, as well as solar radiation field-based model for air pollution studies measured at some DEC monitoring stations (TAPM). It is expected that TAPM in Sydney. The temperature difference simulations will be useful for increasing the between the coast and mainland in understanding of atmospheric processes conjunction with data on solar radiation is associated within this synoptic category. expected to improve the understanding of Future research is to also involve meso-scale flows and the occurrence of investigating the atmospheric processes photochemical smog in Sydney. It is also behind the 30 days, 12% of 241 days within thought that the inclusion of more frequent the category, associated with high pollution upper wind observations from the 6am and occurring in synoptic category 3. It is envisaged that results from this Hyde, R., A. Young M, P. J. Hurley and P. C. research will be useful to Australian Manins (1995). Metropolitan Air Quality regulatory bodies from both a forecast point Study. Meteorology- air movements, of view and for the planning of future Environmental Protection Authority of sources in Sydney and surrounding regions. NSW. Kalkstein, L. S. and P. Corrigan (1986). “A synoptic climatological approach for geographical analysis: assessment of REFERENCES sulfur dioxide concentrations.” Annals of BoM (1991). Climate of New South Wales. the Association of American Canberra, Bureau of Meteorology: 26. Geographers 76(3): 381-395. Cheng, S., H. Ye and L. S. Kalkstein (1992). “An Leighton, R. M. and E. Spark (1995). evaluation of pollution concentrations in Relationship between synoptic Philadelphia using an automated climatology and pollution events in synoptic approach.” Middle States Sydney, Bureau of Meteorology: 57. Geographer 25: 45-51. McGregor, G. R. and D. Bamzelis (1995). Davis, J. M., B. K. Eder, D. Nychka and Q. Yang “Synoptic typing and its application to (1998). “Modeling the effects of the investigation to weather air pollution meteorology on ozone in Houston using relationships, Birmingham, United cluster analysis and generalized additive Kingdom.” Theoretical and Applied models.” Atmospheric Environment Climatology 51: 223-236. 32(14-15): 2505-2520. NEPC (1998). National Environment Protection Eder, B. K., J. M. Davis and P. Bloomfield Measure for Ambient Air Quality. (1994). “An automated classification Canberra, National Environment scheme designed to better elucidate the Protection Council. dependence of ozone on meteorology.” Schreiber, K. V. (2000). A synoptic climatological Journal of Applied Meteorology 33: evaluation of surface ozone 1182-1199. concentrations in Lancaster County, Greene, J. S., L. S. Kalkstein, H. Ye and K. Pennsylvania, Millersville University Smoyer (1999). “Relationships between Environmental Institute/Lancaster synoptic climatology and atmospheric Environmental Foundation: 30. pollution at 4 US cities.” Theoretical and Shahgedanova, M., T. P. Burt and T. D. Davies Applied Climatology 62(3-4): 163-174. (1998). “Synoptic climatology of air Hawke, G. S., A. C. Heggie, R. Hyde, A. Mitchell pollution in Moscow.” Theoretical and and R. Rothwell (1978). Study of an Applied Climatology 61(1-2): 85-102. oxidant day in Sydney. Proceedings of Statheropoulos, M., N. Vassiliadis and A. Pappa the National Clean Air Conference, (1998). “Principal component and Clean Air Society of Australia and New canonical correlation analysis for Zealand, Brisbane, Ann Arbour examining air pollution and Publishers. meteorological data.” Atmospheric Holzworth, G. (1967). “Mixing depths, wind Environment 32(6): 1087-1095. speeds and air pollution potential for Yarnal, B. (1993). Synoptic climatology in selected locations in the United States.” environmental analysis. London, Journal of Applied Meteorology 6: 1039- Belhaven Press. 1044.