广州大气中异戊二烯浓度变化特征、化学活性和来源分析

在广州番禺大气成分站(GPACS)应用在线监测仪器对异戊二烯进行长达1年的观测,获得异戊二烯浓度变化特征、大气化学活性和来源规律.结果表明:广州地区异戊二烯日均浓度为1.12 ppbv,由于受光照和温度影响较大,各月日均浓度在0.07~2.72 ppbv范围内波动.异戊二烯在冬季的日变化规律与其他季节不同,呈现双峰值变化,较大峰值出现在下午14:00,主要受光照和温度影响;较小峰值出现在晚上22:00左右,主要受机动车排放影响.采用最大增量活性(Maximum Incremental Reactivity,MIR)因子加权法和等效丙烯浓度法均发现异戊二烯的大气化学活性在监测的VOCs物种中最强,分别占总活性的15.45%和36.74%.通过异戊二烯与机动车标志性物质3-甲基戊烷、顺-2-丁烯的比值发现,广州地区异戊二烯在冬季夜晚主要来源于机动车排放,在秋季和春季夜晚也受到机动车排放影响,而夏季夜晚受机动车排放最不明显.这主要是由于在冬季、秋季和春季,监测点主要受到来自广州城区污染物输送的影响,而在夏季污染物从广州郊区输送使监测点受机动车排放的影响很小.异戊二烯与3-甲基戊烷、顺-2-丁烯在各季节的白天都没有线性关系,表明白天异戊二烯的排放受机动车的影响不大.

Variation characteristics, chemical reactivity and sources of isoprene in the atmosphere of Guangzhou

In this study, the concentration variation, chemical reactivity and sources of isoprene were characterized by online instrument at Guangzhou Panyu Atmospheric Component Station (GPACS) for a year. The results showed that the daily average concentration of isoprene in the Guangzhou was 1.12 ppbv within the range from 0.07 ppbv to 2.72 ppbv due to the large effect from solar radiation and temperature. In winter, the diurnal variation of isoprene was different from that of other seasons with two peaks: a larger peak at 14:00 from high solar radiation and temperature and a smaller peak at 22:00 from vehicular emission. During the time of measurement, Isoprene had the highest chemical reactivity, accounting for 15.45% and 36.74% of total MIR (Maximum Incremental Reactivity) and K_OH, respectively. The source of isoprene was analyzed by examining the ratios with 3-methypentane and cis-2-butene, two exhaust tracers. It was revealed that at night, isoprene was mostly affected by vehicular emissions in winter, while less affected in autumn and spring and the least affected in summer. This was because the monitoring site was mainly affected by the pollutants from downtown Guangzhou in winter, autumn and spring but was mainly affected by the pollutants from rural areas in summer. Isoprene showed no linear relationships with 3-methypentane and cis-2-butene, suggesting that isoprene was not affected by vehicular emissions during daytime.