土壤环境科学实验室知识库

      挥发性有机物(Volatile organic compound,  VOCs)是大气中极为重要的痕量气体，其中非甲烷碳氢化合物(NMHCs)和醛酮类化合物是对流层臭氧生成的重要前驱体，也称为臭氧前体 VOCs。近年来，我国大气臭氧污染态势呈上升趋势，分析大气臭氧前体 VOCs的组成、活性及来源对明确臭氧浓度增长的原因起重要作用。一些地区，如京津冀、珠三角地区等对臭氧前体 VOCs开展了很多研究，但我国幅员辽阔，不同地区臭氧前体 VOCs的组成差异很大，很多地区对其现状认识不足，如长沙、贵阳等地。因此，本论文率先在贵阳市几个站点进行观测，揭示了观测点臭氧前体 VOCs的主要特征，并通过对长沙市内一个国控点的观测，得到该站点臭氧前体 VOCs的主要特征。本研究采用罐采样方法采集环境空气样品，利用三级冷阱预浓缩-GC/Dean-switch/FID/FID技术，分析  59种  NMHCs，利用 DNPH衍生化-高效液相色谱技术分析醛酮类化合物。主要结果如下：
（1）本研究在贵阳观测得到的     NMHCs总体积分数为(23.06±17.85)×10-9，其中丙烷体积分数最大。观测得到的不同类别 NMHCs的占比为：烷烃(58.77%)＞苯系物(16.41%)＞人为源烯烃(10.84%)＞炔烃(8.86%)＞BVOC(5.12%)。观测得到的 NMHCs总臭氧生成潜势(OFP)为91.51×10-9(体积分数)，其中苯系物对总OFP，烯烃类对总 LOH的贡献最大(约占38%)；总羟基消耗速率(LOH)为6.15s-1贡献最大。观测到的季节变化表现为秋季＞夏季。有机溶剂使用和机动车排放在NMHCs来源贡献中占主导地位，另外存在特殊过程排放蒎烯，待深入研究。
（2）本研究在长沙观测得到的NMHCs总体积分数为(43.31±33.86)×10-9，其中异戊烷体积分数最大。观测得到的不同类别 NMHCs占比为：烷烃(63.49%)＞炔烃(11.49%)＞苯系物(9.29%)＞人为源烯烃(9.26%)＞BVOC(6.47%)。观测到的季节变化表现为冬季＞夏季＞秋季。溶剂使用是主要排放源（约占 22.65%），汽车尾气及油气挥发对 NMHCs的来源贡献相接近，分别占16.61%和16.51%；煤炭/生物质等燃烧过程排放贡献约为 15.53%；存在以 β蒎烯及间对二甲苯为特征物质的未知源，对大气 NMHCs的浓度贡献约占  16.14%。
（3）本研究在贵阳观测得到的总醛酮化合物浓度为(8.66± 4.38)µg/m3，主要污染物为丙酮(5.04 ± 2.91)μg/m3、甲醛(1.40 ± 0.26) μg/m3、乙醛(1.12 ± 0.28) μg/m3 ；三种污染物整体表现为午间(11:00-13:00)浓度突出，且甲醛/乙醛(C1/C2)比值约为1；研究在长沙观测得到的总醛酮化合物浓度为(9.17 ± 3.16)µg/m3，夏季醛酮类3浓度  (11.48 ± 7.41)µg/m3明显高于秋季(6.68   ± 2.72) µg/m，且C1/C2夏季(2.21)＞秋季(1.02)，乙醛/丙醛(C2/C3)秋季(9.64)＞夏季(5.35)，根据比值诊断，在两地观测得到的醛酮类化合物均符合城市地区 C1/C2的比值特征。

    Volatile   organic  compounds   (VOCs)   play   important   roles  in   atmospheric chemistry, which are important precursors  of tropospheric ozone generation. In recent years, ozone concentrations present an uptrend which were frequently over the ambient air  quality standard,  so  it  is  of great  importance  to  investigate the  concentrations, compositions and  source of  VOCs, which could  contribute to  find out  the reason of increase in ozone  level. Some developed regions,  such as the city  of Beijing-Tianjin-Hebei region  and the  Pearl River  Delta region,  have conducted  many researches  on atmospheric VOCs. However, China has a vast territory and the composition of VOCs in different regions  is dissimilar. Other regions have  insufficient understanding of the
status of VOCs, such as  Changsha and Guiyang. Therefore, this paper firstly  revealed the composition,  activity  and source  characteristics of  atmospheric  ozone precursor VOCs in Guiyang through several observations in city and suburb sites. It also revealed the main  characteristics of atmospheric ozone  precursor VOCs in  Changsha over the past 10 years through  the continuous process near a  national control observation sites in  Changsha City.  In  this study,  ambient  air samples  were  collected  using canister sampling   method.   Non-methane   hydrocarbons  were   analyzed   using   GC/Dean-switch/FID/FID coupled  with a three-stage  preconcentration. Aldehydes  and ketones
were analyzed using HPLC. The main results of this work were listed as follows:
（1）    The average mixing  ratio of total  NMHCs in Guiyang  were (23.06 ±  17.85)×10-9 . Propane is the most abundant specie. Alkanes accounted for 58.77% of the total VOCs  concentrations, followed  by  aromatics  (16.41%),  alkenes (10.84%),  alkynes (8.86%), and BVOC (5.12%). The concentrations of NMHCs were high in autumn and low in  summer. The  most active  substances were aromatics  by calculating  OFP and alkenes were the highest active species  by calculating LOH. Aromatics and alkenes are more active than other NMHCs categories. Ordered by OFP and LOH, the explicit active species are  xylene, toluene, Trimethylbenzene, ethylbenzene,  ethylene, isoprene  and pinene. Furthermore, vehicular emissions  is believed the dominant source of  NMHCs in Guiyang.  Industrial and solvent emissions,  as well as the  biomass combustion and coal combustion also contribute to the concentration of NMHCs.
（2）    The average mixing ratio  of total NMHCs in Changsha were (43.31  ± 33.86)×10-9.Alkanes  accounted  for  63.49%  of  the  concentrations,  followed  by  alkynes (11.49%),  aromatics (9.29%),  alkenes  (9.26%),  and BVOC  (6.47%).  The  observed seasonal variation  is expressed  as winter>  summer> autumn. Isopentane  is the  most
abundant specie. Sources apportionment  of NMHCs are conducted by  using principal component analysis (PCA). The results indicated that the solvent evaporation contribute up  to 22.65%,  vehicle  exhaust  and gasoline  evaporation  contribute to  16.61%  and 16.51%, respectively, coal combustion contributes 15.53% and 16.14% of total NMHCs
are attributed to a unknown sources which  characteristic substance are betapinene and p-xylene.
（3）    The average mixing ratio of total carbonyls in Guiyang were 8.66 ± 4.38 µg/m3 .Formaldehyde, acetaldehyde,  acetone are  the most  abundant carbonyls  with average concentrations  of  1.40  ± 0.26  μg/m3,  1.12  ± 0.28  μg/m3 and 5.04  ±  2.91  μg/m3,respectively. Maximum carbonyl  concentrations usually occurred  between 11: 00-13:
00. Guiyang atmospheric formaldehyde/acetaldehyde was 1. The average mixing ratio of total carbonyls in Changsha were 9.17 ± 3.16 µg/m3. The concentrations of carbonyls were high in summer (11.48 ± 7.41 µg/m3 ) and low in autumn (6.68 ± 2.72 µg/m3). The formaldehyde/acetaldehyde  and  acetaldehyde/  propionaldehyde   were  also  high  in summer  and   low   in  autumn   with   2.21>1.02  and   9.64>5.53,  respectively.   The formaldehyde/acetaldehyde in  Guiyang and Changsha were  agreed with that  in other urban areas.