Chemical characteristics and sources of PM_2.5 in Hohhot, a semi-arid city in northern China: insight from the COVID-19 lockdown

Abstract

Abstract. A knowledge gap exists concerning how chemical composition and sources respond to implemented policy control measures for aerosols, particularly in a semi-arid region. To address this, a single year's offline measurement was conducted in Hohhot, a semi-arid city in northern China, to reveal the driving factors of severe air pollution in a semi-arid region and assess the impact of the COVID-19 lockdown measures on chemical characteristics and sources of PM2.5. Organic matter, mineral dust, sulfate and nitrate accounted for 31.5 %, 14.2 %, 13.4 % and 12.3 % of the total PM2.5 mass, respectively. Coal combustion, vehicular emission, crustal source and secondary inorganic aerosols were the main sources of PM2.5 in Hohhot, at 38.3 %, 35.0 %, 13.5 %, and 11.4 %, respectively. Due to the coupling effect of emission reduction and improved atmospheric conditions, the concentration of secondary inorganic components, organic matter and elemental carbon declined substantially from the pre-lockdown (pre-LD) period to the lockdown (LD) and post-lockdown (post-LD) periods. The source contribution of secondary inorganic aerosols increased (from 21.1 % to 37.8 %), whereas the contribution of vehicular emission reduced (from 35.5 % to 4.4 %) due to lockdown measures. The rapid generation of secondary inorganic components caused by unfavorable meteorological conditions during lockdown led to serious pollution. This study elucidates the complex relationship between air quality and environmental policy.

The Variation in Chemical Composition and Source Apportionment of PM2.5 before, during, and after COVID-19 Restrictions in Zhengzhou, China

“…Factor 1 was characterized by the highly explained variations in Ni, Zn, Se, Mg 2+ , Fe, and Mn in the three periods, identified as traffic emissions. Zn is widely used as an additive for lubricants in engines, vehicular tailpipe exhausts [ 45 ], debris from brake wear, and worn tires [ 46 , 47 ]. Factor 2 was dominated by high K + , Ba, and Mg 2+ concentrations, generally indicators of biomass burning [ 48 , 49 ].…”

“…Factor 6 was characterized by high NO 3 − , SO 4 2− , NH 4 + , and OC content, as well as relatively high concentrations of OC. These species are mainly associated with secondary processes [ 46 , 50 ]. Thus, this factor was classified as a secondary aerosol.…”

Measurement report: Characteristics of airborne black carbon-containing particles during the 2021 summer COVID-19 lockdown in Yangzhou, China

“…China has implemented long-term clean air measures to cut down anthropogenic emissions and improve air quality (Ge et al, 2020), resulting in a nationwide reduction of average fine particulate matter (PM2.5, aerodynamic diameter ≤ 2.5 μm) level from 50 μg m -3 in 2015 to 30 μg m -3 in 2020 (Zhou et al, 2022). However, this PM2.5 concentration remains significantly higher than the new World Health Organization (WHO) guideline value of 5 μg m -3 (WHO Global Air Quality Guidelines, 2021).…”

“…Studies on the effects of large-scale and short-term stringent emission control events on air quality in China have been widely deployed, e.g., the 2008 Beijing Olympic Games (Wang et al, 2010;Zhou et al, 2010), the 2015 Asia-Pacific Economic Cooperation (APEC) (Zhu et al, 2015), the 2014 Nanjing Youth Olympic Games (Wang et al, 2022) and the national COVID-19 lockdown in 2020 winter (Huang et al, 2021;Le et al, 2020;Li et al, 2020;Wang et al, 2020) activities have resulted in significant reductions in gaseous pollutants and particulate matter, not only in megacities Jeong et al, 2022;Sun et al, 2020) but also in middle-sized cities (Clemente et al, 2022;Xu et al, 2020) and rural areas (Cui et al, 2021(Cui et al, , 2020Jain et al, 2021). Compared to the decreasing trends observed in most cities worldwide, the level of PM2.5 in Shanghai (Chang et al, 2020), Hohhot (Zhou et al, 2022), and the Northeast of China Plain (Nie et al, 2021) increased unexpectedly. These observations reveal the complex aerosol chemistry of PM2.5 comprising primary and secondary components.…”