The outbreak of COVID-19 raised a question about the relationship between anthropogenic emissions and air pollution, which has aroused heated discussion. Researches on air-quality changes caused by the lockdowns in different areas shows similar substantial reductions in primary emissions. However, regional disparities exist in responses of secondary pollutants to emissions reduction, especially PM_2.5 and O₃.  

Professor Ding Aijun and his team from the Nanjing University explored global air-quality changes during COVID-19 lockdowns and regional disparities in Ozone (O₃) responses to emission reductions. They integrated multiple observational datasets, including global air quality monitoring network and satellite retrievals, to shed more light on the regional differences in interactions between emissions, atmospheric chemistry, and meteorological conditions. This findings were recently published in Atmospheric and Oceanic Science Letters.

“Observational signals of air-quality change were extracted from multi-year ground-based measurements and satellite-retrieved atmospheric composition columns. Ozone shows rising signals in most areas of both East Asia and Europe whereas a non-negligible declining signal exists in North America, despite nitric oxide (NO_x) reductions over the three regions. It indicates significant differences in relations between NO_x and O₃ changes.” says by Prof. Ding.

Furthermore, Ding and his team investigated meteorological and atmospheric chemical drivers behind the different O₃ responses based on analysis data and proxy indicators (HCHO/NO₂) for O₃ photochemical sensitivity diagnosis. They found O₃ responses to NO_x declines can be affected by the primary dependence on its precursors to a certain extent. The O₃ response in Europe fits particularly well with the O₃ sensitivity regimes.

The study points out that meteorological factors are a rather important driver of the O₃ responses, especially air temperature. Apart from weakened titration effects caused by NO_x declines, increased O₃ in East Asia and Europe can be largely dominated by the climatologically warmer temperatures during the lockdowns in 2020. “Still, the contribution of rising temperature can be partly offset by weakened photochemical reactions due to a decline in solar radiation and an increase in relative humidity in southern China and southern Europe. For North America, declines in temperature and substantial increases in humidity can be important contributors to the decreased O₃ over the western coasts.” concludes by Prof. Ding.

This study investigated the impact of meteorological conditions and chemical sensitivity under emission reductions, which further emphasizes the great importance of taking into consideration the regional disparities and synergistic effects of precursor reductions and meteorological influences for scientific mitigation of O₃ pollution.

IMAGE：METEOROLOGICAL AND CHEMICAL DRIVERS ARE THE REASONS BEHIND REGIONALLY DIFFERENT OZONE RESPONSES TO THE COVID-19 LOCKDOWN.

Citation:

Rong Tang , Xin Huang , Derong Zhou , Haikun Wang , Jiawei Xu , Aijun Ding , Global air quality change during the COVID-19 pandemic: Regionally different ozone pollution responses, Atmospheric and Oceanic Science Letters (2020), doi:https://doi.org/10.1016/j.aosl.2020.100015

Link:

https://www.sciencedirect.com/science/article/pii/S1674283420300155