Characteristics of VOCs during haze and non-haze days in Beijing, China: Concentration, chemical degradation and regional transport impact
Characteristics of VOCs during haze and non-haze days in Beijing, China: Concentration, chemical degradation and regional transport impact
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DOI：
10.1016/j.atmosenv.2018.09.037
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发表时间：
2018-12
影响因子：
5
通讯作者：
Wei Wei-Wei;Yue Li;Yating Wang;Shuiyuan Cheng;Litao Wang
中科院分区：
文献类型：
--
作者：
Wei Wei-Wei;Yue Li;Yating Wang;Shuiyuan Cheng;Litao Wang
本文以北京市VOCs为研究对象，通过VOCs监测和WRF-Chem模型模拟，对2015年7月和12月霾日与非霾日VOCs浓度、组成、化学降解及区域输送影响进行了综合对比研究。监测结果显示，7月霾日VOCs（24.5 ± 6.6 ppbv）比非霾日（20.4 ± 7.8 ppbv）高20.1%，但霾日VOCs:CO比非霾日低13.4%。非霾日至霾日VOCs:CO的相对变化与VOCs与OH自由基（KOH）的反应能力呈负相关。结合8:00-14:00期间VOCs:CO的下降和KOH， OH水平从非霾日的0.75 × 106molec/cm3增加到霾日的1.17 × 106molec/cm3。WRF-Chem模拟计算了区域运输对北京VOCs的贡献，7月霾日平均为−0.5 ppbv，非霾日平均为6.3 ppbv。这些分析表明，夏季雾霾日VOCs的化学降解显著，VOCs的区域运输较弱。12月雾霾日VOCs为91.0 ± 37.3 ppbv，非雾霾日为21.4 ± 14.1 ppbv，雾霾日VOCs:CO仍下降21.2%。而VOCs:CO的减少主要来自烷烃、乙炔和c4单键c5烯烃。非霾日至非霾日期间VOCs:CO的相对变化与kohvalue呈正相关，而在霾日和非霾日均未明显发现VOCs的化学降解。模式模拟结果显示，霾日区域运输对VOCs的贡献（4.4-31.0 ppbv）高于非霾日（0.5-6.5 ppbv）。风的输送也解释了冬季雾霾日与非雾霾日VOCs组成和VOCs:CO比值的差异，雾霾日盛行的南风输送的气团污染程度较重，烯烃、芳烃和CO含量较高。
This paper focused on VOCs (referring to C2single bondC12 hydrocarbons) in Beijing and conducted an integrated comparison study on VOCs concentration, composition, chemical degradation and regional transport impact between haze and non-haze days in July and December of 2015, through VOCs monitoring and WRF-Chem modeling simulation. Our monitoring results show that in July VOCs was 20.1% higher in haze days (24.5 ± 6.6 ppbv) than in non-haze days (20.4 ± 7.8 ppbv), but VOCs:CO in haze days was 13.4% lower than the non-haze level. The relative change in VOCs:CO from non-haze days to haze days responded negatively to VOCs reaction ability with OH radical (KOH). Combining VOCs:CO decline during 8:00–14:00 with KOH, OH level was estimated to increase from 0.75 × 106molec/cm3in non-haze days to 1.17 × 106molec/cm3in haze days. WRF-Chem simulations calculate the regional transport contribution to Beijing VOCs, averagely −0.5 ppbv in haze days and 6.3 ppbv in non-haze days in July. These analyses implied a significant VOCs chemical degradation and a weak VOCs regional transport in summer haze days. In December, VOCs reached 91.0 ± 37.3 ppbv in haze days and 21.4 ± 14.1 ppbv in non-haze days, and VOCs:CO still dropped by 21.2% lower in haze days. However, the VOCs:CO decrease was mostly contributed by alkanes, acetylene and C4single bondC5 alkenes. The relative change in VOCs:CO from non-haze days to haze days seemingly responded positively to KOHvalues and VOCs chemical degradation was never explicitly found in both haze and non-haze days. Model simulations obtain a higher regional transport contribution to VOCs in haze days (4.4–31.0 ppbv) than in non-haze days (0.5–6.5 ppbv). The winds transport also explained the difference in VOCs composition and VOCs:CO ratio between haze and non-haze days of winter, for prevalent south winds in haze days transporting air masses of South Beijing and South Hebei that were more polluted and characterized by higher proportions of alkenes, aromatics and CO.