The promotion effect of nitrous acid on aerosol formation in wintertime in Beijing: the possible contribution of traffic-related emissions

Yongchun Liu,Xuefei Wang,Joni Kujansuu,Maofa Ge,Markku Kulmala,Xiaolong Fan,Yuesi Wang,Chaofan Lian,Yonghong Wang,Juha Kangasluoma,Hong He,Weigang Wang,Zeming Feng,Jing Cai,Biwu Chu,Wei Du,Federico Bianchi,Kaspar R Daellenbach,Chao Yan,Bo Hu,Feixue Zheng,Yusheng Zhang,Tuukka Petäj̈ä

doi:10.5194/acp-20-13023-2020

Abstract

Abstract. Secondary aerosols are a major component of PM2.5, yet their formation mechanisms in the ambient atmosphere are still unclear. Based on field measurements in downtown Beijing, we show that the photolysis of nitrous acid (HONO) may promote the formation of organic and nitrate aerosols in winter in Beijing, which is supported by the fact that the mass concentrations of organic and nitrate aerosols linearly increase as a function of HONO consumed from early morning to noon. The increased nitrate content also leads to the formation of ammonium particulate matter through enhancing the neutralization of nitrate and sulfate by ammonia. We further illustrate that during pollution events in winter in Beijing, over 50 % of the ambient HONO may be related to traffic-related emissions, including direct emissions and formation via the reaction between OH and vehicle-emitted NO. Overall, our results indicate that traffic-related HONO may play an important role in the oxidative capacity and in turn contribute to haze formation in winter in Beijing. The mitigation of HONO and NOx emissions from vehicles may be an effective way to reduce the formation of secondary aerosols and severe haze events in winter in Beijing.

Highlights

China is one of several countries suffering from severe pollution of fine particulate matter with diameters of less than or equal to 2.5 μm (PM2.5) (Lelieveld et al, 2015)
This can be explained by both the intense emissions during the heating season, which is supported by the high concentration of primary pollutants including CO, SO2, and black carbon (BC) (Table S1 in the Supplement), and the stagnant meteorological conditions resulting from the low wind speed (< 2 m s−1) and planetary boundary layer (PBL) height in March (Fig. S4a)
We found a good correlation between the increase in the Organic aerosol (OA) and nitrate mass concentrations and the consumed HONO from early morning to noon during the polluted days in winter

Summary

Introduction

China is one of several countries suffering from severe pollution of fine particulate matter with diameters of less than or equal to 2.5 μm (PM2.5) (Lelieveld et al, 2015). The regional air quality has been continuously improving since the central government of China issued the Clean Air Act in 2013 (Vu et al, 2019), the PM2.5 concentration is still significantly higher than that in developed countries (Fu et al, 2014; An et al, 2019). Y. Liu et al.: The promotion effect of nitrous acid on aerosol formation in wintertime in Beijing under unfavorable meteorological conditions (e.g., stagnant atmosphere and high relative humidity) The feedback loop between the meteorological parameters and haze formation plays an important role in the evolution of haze events The feedback loop between the meteorological parameters and haze formation plays an important role in the evolution of haze events (X. Zhang et al, 2018)

Methods

Results

Conclusion