State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China; School of Natural Resources, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China.
State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China; School of Natural Resources, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China.
Environ Pollut. 2023 Sep 15;333:122021. doi: 10.1016/j.envpol.2023.122021. Epub 2023 Jun 18.
Nitrogen dioxide (NO) and sulfur dioxide (SO) are two major air pollutants in urban environment. Emission reduction policies have thus been implemented to improve urban air quality, especially in the metropolises. However, it remains unclear whether the air concentrations of NO and SO in and around large cities follow a same spatial pattern and how their characteristics change over time in response to the emission reductions. Using ground-based monitoring datasets of air NO and SO concentrations in Beijing, China, we tested the hypothesis of urban air pollutant islands and evaluated their seasonal and inter-annual variations during 2015-2022. The results showed that air NO concentrations increased significantly towards the urban core, being in line with the hypothesis of urban air pollutant island, while air SO concentrations showed no such spatial patterns. The urban air NO island varied seasonally, with larger radius and higher air NO concentrations in spring and winter. In response to the emission reduction, the annual mean radius of the urban air NO island showed a rapid decrease from 45.8 km to zero km during the study period. The annual mean air NO concentration at the urban core showed a linear decrease at a rate of 4.5 μg m yr. In contrast, air SO concentration decreased nonlinearly over time and showed a legacy in comparison to the emission reduction. Our findings suggest different urban-rural gradients of air NO and SO concentrations and highlight their distinct responses to the regional reductions of anthropogenic emissions.
二氧化氮（NO）和二氧化硫（SO）是城市环境中的两种主要空气污染物。因此，已经实施了减排政策以改善城市空气质量，尤其是在大都市。然而，目前仍不清楚大城市及其周边地区的空气 NO 和 SO 浓度是否遵循相同的空间模式，以及它们的特征如何随着减排而随时间变化。利用中国北京地面监测的空气 NO 和 SO 浓度数据集，我们检验了城市空气污染物岛假说，并评估了 2015-2022 年期间它们的季节性和年际变化。结果表明，空气 NO 浓度朝着城市核心区显著增加，与城市空气污染物岛假说一致，而空气 SO 浓度则没有这种空间模式。城市空气 NO 岛具有季节性变化，春季和冬季的半径更大，NO 浓度更高。为了响应减排，城市空气 NO 岛的年平均半径在研究期间从 45.8 公里迅速减少到零公里。城市核心区的年平均空气 NO 浓度以每年 4.5μg m yr 的线性速率下降。相比之下，空气 SO 浓度随时间呈非线性下降，与减排相比存在遗留问题。我们的研究结果表明空气 NO 和 SO 浓度的城乡梯度不同，并强调了它们对人为排放区域减排的不同响应。
