Street protests and air pollution in Hong Kong Brimblecombe, Peter Published in: Environmental Monitoring and Assessment Published: 01/05/2020 Document Version: Final Published version, also known as Publisher’s PDF, Publisher’s Final version or Version of Record License: CC BY Publication record in CityU Scholars: Go to record Published version (DOI): 10.1007/s10661-020-8243-0 Publication details: Brimblecombe, P. (2020). Street protests and air pollution in Hong Kong. Environmental Monitoring and Assessment, 192(5), [295]. https://doi.org/10.1007/s10661-020-8243-0 Citing this paper Please note that where the full-text provided on CityU Scholars is the Post-print version (also known as Accepted Author Manuscript, Peer-reviewed or Author Final version), it may differ from the Final Published version. When citing, ensure that you check and use the publisher's definitive version for pagination and other details. 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Download date: 25/09/2021 Environ Monit Assess (2020) 192: 295 https://doi.org/10.1007/s10661-020-8243-0 Street protests and air pollution in Hong Kong Peter Brimblecombe Received: 4 July 2019 /Accepted: 25 March 2020 /Published online: 19 April 2020 # The Author(s) 2020 Abstract June 2019 saw large-scale street protests in Keywords Streetblockage .Traffic diversion .Roadside Hong Kong that impeded traffic flow along streets in air pollution . NO2 . Traffic associated air pollutants areas around to the Legislative Council building. These (TRAP) had the potential to reduce overall air pollutant emis- sions from traffic and lower their concentrations. Two roadside monitoring stations relatively close to the Disrupted traffic flows during large-scale street protests Legislative Council reveal that measured concentrations seem likely to affect local air quality. Although Hong of nitrogen dioxide declined during the protests com- Kong residents are often seen as compliant, there have pared with measurements from other sites by at least been several large-scale public protests since 1997, 50% on many occasions. There were only subtle chang- when it became a special administrative region of es in particulate loads and no evidence of any reduction China. Such protests are mainly driven by concerns over in carbon monoxide concentrations. Pedestrianisation the gradual erosion of autonomy granted to the Hong and bus route rationalisation are often seen as methods Kong Special Administrative Region (HKSAR) as part to reduce exposure in congested areas, but the observa- of a historic agreement between China and the UK. tions here suggest that the substantial improvements in More than seven million people live in the region, which the nitrogen dioxide levels might not be matched by has relatively little habitable land. Population density is improvements in other pollutants. Plans for changes to therefore high, allowing public transport to be very street layouts to improve air quality need careful inves- efficient. This offers the potential for large crowds to tigation before they are implemented. gather rapidly, which in recent years has been enhanced by the prevalence of social media. It is possible for a • Highlights Concentrations of NO2 are reduced over expected million people to gather for an afternoon of protest. values during street protests. Car ownership in Hong Kong is relatively low, but • PM2.5 shows only slight and carbon monoxide no decrease during protests. diesel buses and goods vehicles and taxis (using liquid • Pedestrianisation needs care if to be used as a pollution reduction petroleum gas) are important pollutant sources along the measure. crowded roads in many urban areas. Three roadside air pollution monitoring stations in Hong Kong reveal high P. Brimblecombe concentrations of traffic-derived pollutants that follow School of Energy and Environment, City University of Hong Kong, Kowloon Tong, Hong Kong regular daily and weekly cycles. There are also seasonal changes to air pollutants with the higher concentrations P. Brimblecombe (*) found at the beginning and end of the year, when the Guy Carpenter Climate Change Centre, City University of Hong wind speeds are low and mixing depths are reduced Kong, Kowloon Tong, Hong Kong e-mail: [email protected] (Louie et al. 2005;Aietal.2016). Nitrogen dioxide is 295 Page 2 of 9 Environ Monit Assess (2020) 192: 295 an important roadside pollutant in Hong Kong, often and Kim (2017) make a plausible claim of a 35% exceeding air quality objectives, which may be attribut- decrease of air pollution from the Cheonggyecheon ed to increasing traffic, higher primary emissions of restoration project in Korea, details of this achievement NO2 (Tian et al. 2011) and a heavy vehicle fleet whose are sparse. As Nieuwenhuijsen and Khreis (2016)argue, emissions are higher than expected (Lau et al. 2015). In freeing urban areas of cars ‘is likely to have direct and 2014, protesters carrying yellow umbrellas blocked the indirect health benefits, but the exact magnitude and streets for several months. Media articles suggested that potential conflicting effects are as yet unclear’. the protests could make Hong Kong’s air cleaner, which This paper looks at the pollutant concentrations dur- led to an enduring view that the umbrella movement ing some short-duration public protests in central areas temporarily solved the cities air pollution problems of Hong Kong, using data available from Hong Kong’s (SCMP 2014, Kan, 2015; Cheung 2017). Naturally, Environmental Protection Department (HKEPD) moni- the situation was rather more complex than this (Pan toring stations. The sudden changes in pollutant levels et al. 2017). Some pollutants (most notably nitrogen that occur when streets are blocked during large protests dioxide) were reduced in the early days of the protests, give an opportunity to explore the changes that could and there were subtle changes in the concentrations of arise if traffic reduction plans were implemented (Pan fine particulate materials. Carbon monoxide changed et al. 2017). This work extends a previous study little and ozone increased, because it was no longer (Brimblecombe and Ning 2015), which examined the titrated out by nitric oxide (Brimblecombe and Ning lengthy protest of 2014, examining the brief demonstra- 2015). Nevertheless, correlation analysis revealed that tions that occurred on a number of days in the early the road blockage failed to change the daily cycle of summer of 2019. Later in the year, protests were often PM10 and PM2.5 in the urban area (Lu et al. 2016). After smaller and widely spread across the region, so they the initial stages of the protest, when the nitrogen oxides were more difficult to study. However, it is useful to were at a reduced level, air quality subsequently wors- compare 2019 with some previous events (> 2003) in ened. Part of this was simply seasonal change, although the central parts of Hong Kong. This study aims to draw traffic was effectively redirected along alternate routes lessons about the improvements to air quality and con- to avoid the protests (Brimblecombe and Ning 2015). siders how these might be used to assess likely air Traffic diversions of the kind imposed by protests are quality improvements from pedestrianisation or altering a useful indicator for those planning to pedestrianise or transport flow along streets. change the vehicle mix on streets. Hong Kong has been enthusiastic about pedestrianisation (HKIP 2014), bus route rationalisation and reducing oversupply of buses Method and data sources (Chai 2015; Tang and Lo 2008)aswaysofimproving air quality. However, little research has been done on the The public protests in Hong Kong over the period 2003– impact of such changes on air pollution. If cities are 2019 mentioned here are listed in Table 1.Somestarted made free of cars, then there can be as much as 40% with smaller events, but public participation grew over reduction in NO2 (Nieuwenhuijsen and Khreis 2016). time and ultimately led to large gatherings. The number The improved air quality from better traffic flow, green of participants is often disputed. The lower numbers in waves or one-way systems may be short-lived if traffic the table refers to the official values, from the police, flow increases because of reduced congestion (Joumard which try to represent the maximum number of people et al. 1996). Restrictions can be applied to some urban at the peak of the gathering. The larger values are areas such as imposed by traffic diversions (Walker et al. estimates from the organisers and aim to account for 1999; Clench-Aas et al. 2000) or through congestion the total number of people involved and appear to be charges, but the changes may be subtle (Beevers and confirmed by independent observers. Carslaw 2005;Atkinsonetal.2009). Much is written The location of the protests and the nearby HKEPD about the potential benefits of pedestrianisation (Soni monitoring sites are shown in Fig. 1.Datafromthese and Soni 2016) to reduce air pollution (Kan 2015; stations are available at http://epic.epd.gov. Maliene et al. 2018; Yassin 2019), but these seem to hk/EPICDI/air/station/?lang=en. General stations, derive more from enthusiasm than measured data, so effectively urban background sites, are present at (i) further studies are clearly needed.