The shifting of secondary inorganic aerosols formation mechanism during haze aggravation: The decisive role of aerosol liquid water

Abstract

Abstract. Although many considerable efforts have been done to reveal the driving factors on haze aggravation, however, the roles of aerosol liquid water (ALW) in SIAs formation were mainly focused on the condition of aerosol liquid water content (ALWC)<100 μg/m3. Based on the in-situ high-resolution field observation, this work studied the decisive roles and the shifting of secondary inorganic aerosols formation mechanism during haze aggravation, revealing the different roles of ALWC in a broader scale (~ 500 μg/m3) in nitrate and sulfate formation induced by aqueous chemistry in ammonia-rich atmosphere. The results showed that chemical domains of perturbation gas limiting the generation of secondary particulate matters presented obvious shifts from HNO3 sensitive to HNO3 and NH3 co-sensitive regime with the haze aggravation, indicating the powerful driving effects of ammonia in ammonia-rich atmosphere. When ALWC<75 μg/m3, the sulfate generation was preferentially triggered by the high ammonia utilization, then accelerated by nitrogen oxide oxidation from Clean to Moderate pollution stages, characterizing as NOR<0.3, SOR<0.4, NTR<0.7 and the moral ratio of NO3-:SO42-=2:1. While ALWC>75 μg/m3, aqueous-phase chemistry reaction of SO2 and NH3 in ALW became the prerequisite for SIAs formation driven by Henry’s law in the ammonia-rich atmosphere during Heavy and Serious stages, characterizing as high SOR (0.5–0.9), NOR (0.3–0.5), NTR (>0.7) and the moral ratio of NO3-:SO42-=1:1. A positive feedback of sulfate on nitrate production was also observed in this work. Our results provided the evidence for the response of the transition ALWC with seasonal variability and climate change. It implies the target controlling of haze should not simply focus on SO2 and NO2, more attention should be paid on gaseous precursors (e.g., SO2, NO2, NH3) and aerosol chemical constitution during different haze stages.