The impacts of VOCs on PM2.5 increasing via their chemical losses estimates: A case study in a typical industrial city of China

Volatile organic compounds (VOCs) have been explicitly required to be controlled by national or local governments to tackle heavy PM 2.5 pollution in China. However, the role of VOCs chemistry in PM 2.5 is still far away from being fully understood. In this study, we selected a typically industrialized city of China, conducted VOCs online measurements in July and December of 2020, estimated VOCs chemical losses, and explored their impacts on PM 2.5 in the real atmosphere. Our measurements totally detected the mixing ratios of 53 VOCs species, sum of which reaching 20.8 ± 9.1 ppb and 45.5 ± 19.8 ppb in July and December respectively. Based on the change in the relative abundance of various VOCs species with different reactivity, daily OH exposure and daily O 3 exposure (molecules·s·cm −3 ) were estimated, respectively with the mean value of 11.0 × 10 10 and 5.2 × 10 15 in July, 5.9 × 10 10 and 3.1 × 10 15 in December. Thus, there were about 6.7 ± 3.2 ppb and 11.1 ± 5.0 ppb VOCs chemically lost in July and December, with the average loss ratio of 29.7% and 19.3% in respective. In July, PM 2.5 in the range of 20–60 μg m −3 positively responded to VOCs loss ratios, and high PM 2.5 values were always accompanied by higher VOCs losses instead of high CO levels; but their relationship became negative in December when PM 2.5 in the range of 40–150 μg m −3 , and extremely high PM 2.5 values happened in high CO conditions instead of high VOCs losses conditions. Moreover, PM 2.5 measurements in this city also showed an apparent upward trend in OC/EC with PM 2.5 in summer, but a slight downward trend in winter. These all indicated that in the conditions of stronger solar radiations (summer) and low-middle aerosol loads, VOCs chemistry played the important role in PM 2.5 increasing through contributing SOA; but in the conditions of lower solar radiations (winter) and heavy aerosol loads, VOCs chemistry was greatly weakened and had the minor impact on PM 2.5 increasing. The measure involving VOCs reduction to alleviate PM 2.5 pollution in winter needs to be cautiously considered and examined. • Chemical losses of VOCs in a typical industrial city were estimated. • The total loss ratio reached 29.7 ± 9.0% and was positively related to PM 2.5 in summer. • The total loss ratio reached 19.3 ± 7.4% but was negatively related to PM 2.5 in winter. • OC/EC ratio increased with PM 2.5 in summer but decreased with PM 2.5 in winter. • VOCs chemistry contributed to PM 2.5 increasing in summer but not in winter.