AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
High Time Resolution Observation and Its Source Apportionment of Brown Carbon during Winter and Summer in Urban Xi'an, Northwestern China
YALI LEI, Zhenxing Shen, Tian Zhang, Di Lu, Yaling Zeng, Qian Zhang, Hongmei Xu, Jianhuai Ye, Yiming Qin, Xin Wang, Junji Cao, Xi'an Jiaotong University
Abstract Number: 313 Working Group: Source Apportionment
Abstract There is a growing evidence suggesting that an enhancement of brown carbon (BrC) in the severe haze episodes. In this study, hourly measurements of BrC in PM2.5 were conducted in Xi’an, a typical city in Northwestern China, during the winter (1 January to 6 January) and the summer (24 July to 5 August) of 2017. Filters were extracted in methanol. The light-absorbing properties of the solution were quantified using UV-vis spectroscopy. Results showed that the absorption coefficient at 365 nm (b365, methanol) in winter was over 7 times higher than that in summer, while the mass absorption cross-section (MAC365, methanol) in winter for BrC was nearly double of that in summer. During the winter haze days, the average b365, methanol peaked at 00:00 am LT with the lowest values observed at 7:00 am LT in the morning, contrary to the high afternoon and low nighttime levels observed in non-haze days. Unlike the diurnal patterns in winter, average summer babs365, methanol diurnal variation presented high mid-day and low afternoon levels in haze days. However, in non haze days, the pattern showed morning high levels and night low levels. Source apportionment of babs365, methanol based on the positive matrix factorization receptor model and multiple linear regressions showed the babs365, methanol of secondary formation accounted for 28.0 % (winter) and 74.5 % (summer) of total babs365, methanol, indicating that secondary formation was an important contributor to BrC emissions over Xi’an during both winter and summer.