Spatiotemporal variations of ambient volatile organic compounds and their sources in Chongqing, a mountainous megacity in China

• Published in: The Science of the total environment Vol. 627; pp. 1442 - 1452
• Main Authors: Li, Jing, Zhai, Chongzhi, Yu, Jiayan, Liu, Ruilin, Li, Yaqi, Zeng, Limin, Xie, Shaodong
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.06.2018
• Subjects: Chongqing; Online observation; PMF model; Pollutants control; VOCs; Chongqing; VOCs; PMF model; Pollutants control; Online observation
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2018.02.010

Chongqing is the largest megacity in southwest China and has a mountainous and humid climate. Online measurements of 96 volatile organic compound (VOC) species were performed at the three sites JYS, CJZ, and NQ, which are located in the northern, central, and southern sections of the Chongqing urban district, respectively. The measurements were performed from August to September 2015, at a time interval of 1h. The spatiotemporal variation of VOC sources in Chongqing was characterized by combining the positive matrix factorization (PMF) model with the online measurement data. The average total VOC mixing ratios of the CJZ, NQ, and JYS sites were 41.2, 34.1, and 23.0ppbv, respectively. The mixing ratios of tracers of incomplete combustion, exhibited obvious bimodal profiles at the CJZ and NQ sites, whereas those at the JYS site exhibited little change throughout the day. Isoprene at the three sites followed a similar pattern of average diurnal variations in mixing ratios, with minimums before sunrise and maximums at noon. The dominant sources of acetaldehyde and acetone were secondary anthropogenic source and aged air mass transport, respectively, in the city of Chongqing. Seven sources were apportioned to the results of PMF calculation using spatiotemporal VOCs composition data. The Vehicle-related sources were the largest contributor at CJZ and NQ, contributing 44% and 37% of the total VOC mixing ratios, respectively, and exhibited clear diurnal variations. Aged background air, with 68% of total VOC emissions, dominated the VOC emissions at JYS. Solvent utilization was a very important contributor at NQ and coincided with the higher levels of aromatics. O3 formation was generally VOC-limited at NQ and CJZ, and was NOx-limited and transition region alternatively at JYS. Alkenes were important for the O3 formation at CJZ, and both alkenes and aromatics were important for the O3 formation at NQ. [Display omitted] •Ambient VOCs were measured by an online GC/MS-FID system.•VOC compositions and diurnal variations of measured VOCs were discussed.•Vehicle exhaust was a very important source in controlling VOC emissions.•Alkenes have high O3 formation effects.