Air Quality During COVID-19 Lockdown in the Yangtze River Delta and the Pearl River Delta: Two Different Responsive Mechanisms to Emission Reductions in China

Abstract

Despite the large reduction in anthropogenic activities due to the outbreak of COVID-19, air quality in China has witnessed little improvement and featured great regional disparities. Here, by combining observational data and simulations, this work aims to understand the diverse air quality response in two city clusters, Yangtze River Delta region (YRD) and Pearl River Delta region (PRD), China. Though there was a noticeable drop in primary pollutants in both the regions, differently, the maximum daily 8 h average ozone (O 3 ) soared by 20.6–76.8% in YRD but decreased by 15.5–28.1% in PRD. In YRD, nitrogen oxide (NOx) reductions enhanced O 3 accumulation and hence increased secondary aerosol formation. Such an increment in secondary organic and inorganic aerosols under stationary weather reached up to 36.4 and 10.2%, respectively, which was further intensified by regional transport. PRD was quite the opposite. The emission reductions benefited PRD air quality, while regional transport corresponded to an increase of 17.3 and 9.3% in secondary organic and inorganic aerosols, respectively. Apart from meteorology, the discrepancy in O 3 –VOCs–NOx relationships determined the different O 3 responses, indicating that future emission control shall be regionally specific, instead of one-size-fits-all cut. Overall, the importance of regionally coordinated and balanced control strategy for multiple pollutants is highly emphasized.

Typhoon-boosted biogenic emission aggravates cross-regional ozone pollution in China

“…The summertime extreme O 3 pollution in eastern China has been long attributed to fast photochemical production of intensive anthropogenic NO x and VOC emissions under intense solar radiation ( 13 , 20 , 27 ). Moreover, southern China settles a large area of forest, just between YRD and PRD, which releases tremendous biogenic VOCs (BVOCs) as additional O 3 precursors ( Fig.…”

“…Meteorological parameters including incident sunlight and air temperature modulate the O 3 formation, accumulation, and transport (13,23,24). The extreme O 3 pollution generally outbreaks in summer and has been proven to be closely linked to high air temperature and strong solar radiation together with stagnant weather conditions (24)(25)(26)(27)(28). Recent observations have identified O 3 mixing ratios in cities of eastern China well in excess of present air quality standards under the influence of Northwest Pacific typhoon, a frequent weather activity in warm seasons (29)(30)(31)(32)(33).…”

The Impact of COVID-19 Lockdowns on Air Quality—A Global Review

“…In different regions, the maximum daily 8 h average ozone (O 3 ) soared by 20.6-76.8% in YRD but decreased by 15.5-28.1% in PRD. In YRD, nitrogen oxide (NO x ) reductions enhanced O 3 accumulation and, hence, increased secondary aerosol formation [64].…”

Assessment of Sectoral NOx Emission Reductions During COVID‐19 Lockdown Using Combined Satellite and Surface Observations and Source‐Oriented Model Simulations

“…While observational analysis combined with CTMs could estimate total NO x emission reductions, deducing emission reductions from individual emission sectors is more challenging. Real‐time monitoring data such as the traffic flow (Liu et al., 2020; Lv et al., 2020) and continuous stack emissions (Liu et al., 2020), and social economy information (Huang et al., 2020; Wang et al., 2021) were used to estimate the NO x emission changes in transportation, power generation and industries. However, these activities and emission monitoring data‐based techniques are usually limited by data availability (e.g., vehicle fleet composition information) and the timeliness in data reporting (e.g., industrial productions) and may not be suitable to derive emission changes in an entire geographical area.…”