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- Title
Insights into the chemical composition of summertime PM<sub>2.5</sub> at the northeast of the Qinghai-Xizang (Tibet) Plateau.
- Authors
Xu, J.; Zhang, Q.; Wang, Z.; Yu, G.; Ge, X.; Qin, X.
- Abstract
Aerosol filter samples were collected at a high-elevation mountain observatory in the northeastern part of the Qinghai-Xizang (Tibet) Plateau (QXP) during summer 2012 using a low-volume sampler and a micro-orifice uniform deposit impactor (MOUDI). The aim was to improve our understanding of the chemical composition of free tropospheric aerosols in the QXP region. The samples were analyzed for water-soluble inorganic ions (WSIs), organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC), and total organic nitrogen (TON). The bulk chemical composition and the average oxidation degree of water-soluble organic matter (WSOM) were assessed using a high resolution time-of-flight aerosol mass spectrometer. Furthermore, the concentrations of both primary organic aerosol (POA) and secondary organic aerosol (SOA) were estimated. The average mass concentration of the sum of the analyzed species in PM2.5 (WSIs + OC + EC + TON) was 3.74 µg m-3, 36.2% of which was sulfate, 17.8% OC, 16.9% nitrate, 10.1% ammonium, 6.6% calcium, 6.4% TON, 2.6% EC, 1.5% sodium, 0.9% chloride, 0.5% magnesium, and 0.3% potassium. The size distribution of sulfate and ammonium peaked in the accumulation mode (0.32-0.56 µm), whereas the size distributions of both nitrate and calcium peaked in the range of 1.8-3.2 µm, suggesting the formation of nitrate on mineral dust. OC, EC and TON were also predominantly found in the accumulation mode. High average ratios of OC / EC (7.6) and WSOC / OC (0.79) suggested that organic aerosols were primarily made of secondary species. WSOM was found to be highly oxidized in all PM2.5 samples with the average oxygen-to-carbon atomic ratio (O / C) being 1.16 and organic mass to carbon ratio (OM / OC) being 2.75. The highly oxidized WSOM was likely related to active cloud processing during upslope air mass transport coupled with strongly oxidizing environments caused by snow/ice photochemistry. SOA was estimated on average accounting for 75.3% (46.4-96.4%) of the PM2.5, indicating that SOA accounted for a significant portion of the free tropospheric aerosols over the northern QXP.
- Subjects
TIBETAN Plateau; PARTICULATE matter; TROPOSPHERIC aerosols; TIME-of-flight spectrometers; PARTICLE size distribution; MASS transfer
- Publication
Atmospheric Chemistry & Physics Discussions, 2015, Vol 15, Issue 1, p1307
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acpd-15-1307-2015