Chemical Characteristics and Source Apportionment of Typical High Mountain Precipitation in the Hengduan Mountains Area
This study analyzed 75 precipitation samples collected from August 2017 to August 2018 in the Meili Snow Mountain region of the Hengduan Mountains. The chemical characteristics of inorganic ions and their seasonal variations between monsoon and non-monsoon periods were examined. The volume-weighted mean total ion concentration was 246.2 μeq·L–1, with higher concentrations in the non-monsoon season and lower in the monsoon season. The dominant water chemistry type was HCO3–-Ca2+. Principal component and partial correlation analyses indicated that Ca2+, Mg2+, HCO3–, and SO42– mainly originated from local sedimentary rock dust, while Na+ and Cl– were primarily marine during the monsoon, with reduced marine influence in the non-monsoon period. NO3– was largely attributed to South Asian pollution emissions, with significant contributions from biomass burning to K+, Na+, and Cl– in the pre-monsoon phase. PMF source apportionment confirmed that during the monsoon, approximately 70% of Cl– and Na+ were from sea salt, whereas in the non-monsoon, over half came from biomass burning. NO3– was almost entirely from fossil fuel combustion during the monsoon (96%), decreasing to 72% in the non-monsoon. Ca2+ and Mg2+ were mainly from carbonate dust in the monsoon and weathered dust in the non-monsoon. Backward trajectory analysis showed that the non-monsoon period was dominated by westerly transport (60%), while the monsoon was dominated by southwest monsoon transport (81%). These findings provide scientific basis for understanding atmospheric pollution and background values in the region.