Impact of Formation Pathways on Secondary Inorganic Aerosol During Haze Pollution in Beijing: Quantitative Evidence From High‐Resolution Observation and Modeling

Abstract

Abstract Secondary inorganic aerosol (especially SNA: sulfate, nitrate, and ammonium) formed from different pathways, account for significant proportions of ambient particulate matter during haze events. For the first time, we quantitatively explored contributions from different SNA formation pathways by an online monitoring AMS instrument and 3‐dimension factor analysis PMF3 model, which is called “SNA formation pathway apportionment”. Three formation process were identified: NH 4 NO 3 heterogeneous phase reactions (NH 4 NO 3 ‐heter), (NH 4 ) 2 SO 4 gas phase reactions ((NH 4 ) 2 SO 4 ‐gas), and mixed NH 4 NO 3 and (NH 4 ) 2 SO 4 aqueous phase processes (S&N‐aque). Their overall contributions to SNA were 25.7%, 22.1%, and 52.2%, respectively. Moreover, (NH 4 ) 2 SO 4 ‐gas contributed mainly in clean (52.1%); S&N‐aque got the highest contribution in haze episode (69.6%); while sulfate gas phase formations were also found in haze stage (10.3%). The quantitative findings from this work provide hard evidence that aqueous phase processes (including sulfate aqueous phase reactions and nitrate gas‐particle partition) were major drivers for SNA increasing.