Spatiotemporal Ozone Level Variation in Urban Forests in Shenzhen, China

Abstract

This study is among the first to investigate ozone levels in urban forests in China. It establishes that urban forest air quality in Yuanshan Forest Park (Shenzhen) is suitable for recreational activities and identifies spatial, seasonal, and diurnal O3 patterns and relationships with micrometeorological parameters, suggesting the possibility of manipulating relevant forest characteristics to reduce Surface ozone (O3) levels. An understanding of O3 levels of urban forest environments is needed to assess potential effects on human health and recreational activities. Such studies in China are scarce. This study investigated urban forest O3 levels to improve understanding and support residents engaging in forest recreational activities. We monitored O3 levels in 2015–2016 for three urban forests representing common habitats (foothill, valley, and ridge) in Yuanshan Forest Park and for an adjacent square. The overall mean daily and daily maximum 8 h mean (MDA8) O3 concentrations were highest for the ridge forest and lowest for the valley forest. Each forest’s O3 concentrations were highest in summer. Diurnally, forest O3 concentrations peaked between 13:00 and 17:00 and reached a minimum between 03:00 and 09:00. The correlation between forest O3 concentrations and air temperature (AT) was strongly positive in summer and autumn but negative in spring. In each season, O3 concentration was negatively correlated with relative humidity (RH). No MDA8 or hourly O3 concentrations in the forests exceeded National Ambient Air Quality Standard Grade I thresholds (100 and 160 μg m−3, respectively). O3 accumulation is present in ridge urban forest in all seasons. Foothill and valley urban forests have better air quality than ridge forestation. Urban forest air quality is better in spring and autumn than in summer and is better from night-time to early morning than from noon to afternoon.

Spatiotemporal Assessment of Atmospheric Pollutants in Yancheng City, Eastern Coastal City of China

“…However, this result was quite different from the observation that the highest ρ(O 3 ) was observed in summer when solar radiation was the strongest, in cities such as Beijing [16], Chengdu [17] and Shenzhen [18]. During autumn and winter, with the decrease of temperature and solar duration, ρ(O 3 ) decreased gradually, reaching the minimum value in winter [18]. However, other pollutants such as PM 2.5 , PM 10 , NO 2 , SO 2 and CO reached the maximum values in winter due to the low temperature, calm and steady weather, easy occurrence of temperature inversion, high humidity and calm wind in winter [17].…”

“…This was the main reason that contributed to the lower ρ(O 3 ) in summer, even at higher solar radiation than in spring. However, this result was quite different from the observation that the highest ρ(O 3 ) was observed in summer when solar radiation was the strongest, in cities such as Beijing [16], Chengdu [17] and Shenzhen [18]. During autumn and winter, with the decrease of temperature and solar duration, ρ(O 3 ) decreased gradually, reaching the minimum value in winter [18].…”

Impact of Urban Forest and Park on Air Quality and the Microclimate in Jinan, Northern China

“…Sicard et al [26], meanwhile, found that urban trees reduced the O 3 in 2010 by 5.4 g m −2 yr −1 in 55 US cities and 3.7 g m −2 yr −1 in 86 Canadian cities. In contrast, Duan et al [27] found that O 3 concentrations in urban forest areas were higher than those in the urban center, which is in agreement with the findings of Yli-Pelkonen et al [28] and Grundstrom and Pleijel [29]. Thus, more research is needed to understand whether urban vegetation ultimately increases or decreases O 3 concentrations.…”

“…In addition, as an important precursor of O 3 , the distribution of NOx in urban centers is much higher than that in forest areas around cities, resulting in a shift of the formation regime of O 3 from the VOC-limited regime in urban centers to a transitional regime in urban forest areas [22]. Studies have shown varying results regarding whether urban vegetation ultimately increases or decreases O 3 concentrations [25][26][27][28][29]. Fares et al [25] estimated a total annual removal of 8.4 and 8 kg per hectare for PM 10 in two urban parks in Rome and Turin, Italy, and the trees in the two urban parks were found to remove 8.1 and 1.42 kg O 3 per hectare.…”

Air pollutant removal by urban vegetation: A meta-analysis of gaps in research and environmental management

“…Optimally, in urban areas, controlling both the emission sources of botanical VOCs and transport NOx can more effectively minimize O3 production 46 , since O3 pollution gradually becomes the main air pollutant in megacities with high greenspace coverage, including in Shenzhen 45,77,78 .…”