| Popis: |
The ubiquitous presence of organic aerosols (OA) and their dominant role in climate forcing via direct and indirect effects are increasingly recognized. Among the large spectrum of OAs, water-soluble secondary organic aerosols (SOA) have gained considerable scientific interest due to the in-cloud formation process and consequent climate effects. However, a lack of consensus on the molecular fingerprints and formation pathways of SOA limits our ability to assess their climate impact globally.In this study, a detail investigation is made on water-soluble SOA components such as dicarboxylic acids, oxocarboxylic acids and dicarbonyls in springtime (March to May 2019) PM10 samples collected from a remote high-altitude site Lachung (27.4˚N and 88.4˚E, 2700 m a.s.l.) in the eastern Himalayas. The molecular fingerprints of water-soluble SOA components showed the predominance of oxalic acid (C2) followed by phthalic (Ph) and succinic acid. The diagnostic mass ratio of Ph to azelaic (C9) acid (2.1-7.7) indicated that anthropogenic emissions are the major sources of water-soluble OA at this remote high-altitude site. Moreover, SO42- dominates total water-soluble inorganic constituents and correlates significantly (R2 = 0.66) with the ISORROPIA-II model-derived aerosol liquid water content (LWC), indicating a crucial role of anthropogenic SO42- in controlling LWC of aerosols over the eastern Himalayas. Notably, we found significant positive relationships of C2 acid with both SO42- (R2 = 0.94) and aerosol LWC (R2 = 0.76), suggesting oxalic acid formation in LWC-enriched aerosols largely controlled by anthropogenic SO42- via aqueous phase photochemical processes. The increased formation of oxalic acid and related polar compounds with increasing SO42- is indicative of the fact that the reduction in anthropogenic emissions at the regional scale or source regions could control the water-soluble SOA loading in the atmosphere of the eastern Himalayas. |
