张家界森林大气中醛酮类化合物浓度变化特征

Variation Characteristics of Atmospheric Carbonyl Compounds in Zhangjiajie Forest

为探究中亚热带森林大气中醛酮类化合物浓度变化特征,于2014年8月—2015年1月在张家界森林公园采用EPA TO-11A方法对张家界森林大气中醛酮类化合物质量浓度进行了监测.结果表明:张家界森林大气中主要的醛酮类化合物为甲醛、乙醛、丙酮、丙醛和MACR(甲基丙烯醛),质量浓度分别为4.32、0.95、3.01、0.48和0.51μg/m3.大气中ρ(甲醛)、ρ(乙醛)和ρ(MACR)的季节变化特征很明显,夏季和秋季醛酮类化合物质量浓度较高,冬季醛酮类化合物质量浓度较低.此外,醛酮类化合物质量浓度日变化显著,除了10月、12月受人为因素影响较大外,其余月份醛酮质量浓度最大值通常出现在13:00—15:00.张家界森林大气中C1/C2(ρ(甲醛)/ρ(乙醛))为5.72,比城市地区(C1/C2为1左右)高,但比偏远森林地区(C1/C2为10左右)低.ρ(甲醛)与ρ(乙醛)、ρ(MACR)均呈正相关且达到显著水平,而ρ(丙酮)与ρ(甲醛)、ρ(乙醛)与ρ(MACR)的相关性差.与文献报道的加拿大Ontario、墨西哥Langmuir等地区对比,张家界森林大气中醛酮类化合物质量浓度较高,但明显低于北京、上海等城市地区.研究显示,张家界森林大气中甲醛、乙醛和MACR主要来自森林地区植物排放的VOCs光氧化生成,丙酮除了来自植物排放的有机物光氧化分解外,还有其他人为源,进一步说明了张家界森林大气中醛酮类化合物浓度变化主要受光化学反应等自然影响,但人为因素的影响也不容忽略.

The atmospheric carbonyls in Zhangjiajie forest were measured by using EPA TO-11A from August 2014 to January 2015. Formaldehyde, acetaldehyde, acetone, propionaldehyde and methacrolein （MACR） were found to be the most abundant carbonyls, with average concentrations of 4.32, 0.95, 3.01 , 0.48 and 0. 51 μg/m^3 , respectively, ρ（ formaldehyde ） , ρ （ acetaldehyde ） and ρ（MACR） seasonally changed; the concentrations of carbonyls were high in summer and autumn and low in winter. The daily concentrations of carbonyls changed significantly too. Except in October and December when human factors were greater, maximum earbonyl concentrations usually occurred between 13：00-15：00. Zhangjiajie forest atmospheric C1/C2 was 5.72, which was higher than in urban areas （where C1/C2 is about 1 ）, but lower than remote forest areas （where C1/C2 is about 10）. ρ （formaldehyde）, ρ（acetaldehyde） and ρ（MACR） were positively correlated, and reached a significant level, while ρ （acetone） and ρ （formaldehyde）, p（acetaldehyde） and p（MACR） had poor correlation. Compared with other regions such as Ontario in Canada and Langmuir in Mexican, the concentrations of earbonyls in Zhangjiajie forest atmosphere were higher, but significantly lower than urban areas of Beijing and Shanghai. The study showed the Zhangjiajie forest atmospheric formaldehyde, acetaldehyde and MACR were mostly from photochemical reactions of plant VOC emissions in forest areas, but sources of acetone were not only from photochemical reactions of plant VOCemissions but also other human-made sources. The study further showed that the change of carbonyl concentrations in Zhangjiajie forest atmosphere were mainly influenced by photochemical reactions in natural forest, but human factors couldn＇ t be ignored.