Analysis of Volatile Organic Compound Measurements During COVID-19 Lockdowns in Changzhou, China: Source Attribution and Emissions Reductions

Abstract:

Following the spread of the novel coronavirus disease (COVID-19), many countries enacted large-scale lockdowns in 2020. Reductions in vehicle traffic, industrial activity, and energy consumption led to reductions in respective emissions of atmospheric pollutants. These episodes provide a test case to study air quality given these reduced anthropogenic emissions and allow a better understanding of possible impacts of future pollutant control policies. Here, we present measurements of volatile organic compounds (VOCs) in Changzhou, a Chinese city in the Yangtze River Delta. These measurements were made by a prototype compact Vocus proton-transfer-reaction time-of-flight mass spectrometer (Vocus-PTR-TOF-MS) with a mass resolving power m/Δm of 950 and detection limits on the order of 20 pptv over a 1-minute averaging period. These measurements span from January 8 through March 27, 2020, including periods of pre-lockdown, level-I response where the lockdown was in full effect (beginning January 25), and level-II response where the lockdown was eased and work slowly resumed (beginning February 25). These measurements do not include the post-lockdown period (beginning April 1). We present a Positive Matrix Factorization (PMF) analysis of these VOCs and quantify the reduction in the emission sources found by PMF during the different phases of the COVID-19 lockdown. At this location, NO, NO₂, O₃, CO, SO₂, PM_2.5 and PM₁₀ were also measured during the same time period. Comparisons between these measurements and those made at other monitoring stations in and around Changzhou suggest air masses sampled at our measurement location are representative of the larger Changzhou region, and we also quantify the changes in these species during the level-I and level-II responses.