Organosulfates in Humic-like Substance Fraction Isolated from Aerosols at Seven Locations in East Asia: A Study by Ultra-High-Resolution Mass Spectrometry
详细信息 查看全文
- 作者：Peng Lin ; Jian Zhen Yu ; Guenter Engling ; Markus Kalberer
- 刊名：Environmental Science & Technology (ES&T)
- 出版年：2012
- 出版时间：December 18, 2012
- 年：2012
- 卷：46
- 期：24
- 页码：13118-13127
- 全文大小：395K
- 年卷期：v.46,no.24(December 18, 2012)
- ISSN：1520-5851
文摘
Humic-like substances (HULIS) in ambient aerosols collected at seven locations in East Asia were analyzed using electrospray ionization (ESI) coupled with an ultra-high-resolution mass spectrometer (UHRMS). Locations included a 3 km high mountaintop site in Taiwan, rural, suburban, and urban locations in the Pearl River Delta (PRD), South China, and in Taiwan. Organosulfates (OS) in the HULIS fraction were tentatively identified through accurate mass measurements and MS/MS spectra interpretation. In the two mountaintop samples collected in regional background atmosphere, little OS were detected, while a few hundred OS formulas were identified in the six samples taken in Taiwan and PRD. Many of the OS ions were among the most intense peaks in the negative ESI鈥揢HRMS spectra, and their elemental formulas were identical to OS derived from biogenic volatile organic compounds (BVOCs) (e.g., monoterpenes) that have been identified in chamber studies. With OS having less than 6 carbon atoms too hydrophilic to be effectively retained in the HULIS fraction, OS containing 10 carbon atoms were the most abundant, indicating monoterpenes as important precursors of OS in the HULIS fraction. Clear spatial variation in abundance of OS was found among different atmospheric environments, with enhanced coupling of BVOCs with anthropogenic acidic aerosols observed in the PRD samples over the Taiwan samples. The double bond equivalent (DBE) values indicate the majority of OS (>90%) in the HULIS fraction are aliphatic. The elemental compositions of OS compounds containing N atoms (defined as CHONS) indicate that they are probably nitrooxy OS. Some insights into OS formation mechanisms are also gained through examining the presence/absence of perceived reactant鈥損roduct formula pairs in the mass spectra. The results suggest the dominant epoxide intermediate pathway for formation of OS compounds without N atoms (defined as CHOS) and confirm the more readily hydrolyzed characteristics of the 鈭扥NO2 group than the 鈭扥SO3 group. There is a lack of evidence for the epoxide pathway to account for the formation of OS in the CHONS subgroup.