Characterization and speciation of non-methane hydrocarbons (NMHCs) and their implications on the atmosphere of South China

Abstract

South China has experienced rapid economic growth, fast industrialization and urbanization in the last two-three decades. The excessive uses of resources, dramatic changes of land use pattern and rapid increases of motor vehicles and industries have resulted in severe degradation of air quality both in the urban and rural areas of the region. Non-methane hydrocarbons (NMHCs) are among the most important constituents in the atmosphere. They play crucial roles in atmospheric chemistry and the formation of tropospheric ozone and other secondary pollutants. This thesis investigates the characterization and Speciation of NMHCs in the fast changing South China region with an aim to assess their implications on its atmosphere. A large pool of ambient and source NMHC data was obtained for the first time in various environments of South China, extending from less developed Yunnan and Hainan Provinces to more developed Guangdong and Zhejiang Provinces. Evolution of the characteristic NMHC profiles in representative atmospheric environments in South China through this study will greatly enhance our knowledge in these important ozone precursors. The source and source regions of these Ci-Cio NMHC species were assessed through comparison of the profiles and characteristic ratios of NMHC species in ambient and source samples. Tools such as backward air trajectory and satellite images are utilized. Analysis of characteristic spectra in these regions unveiled that there were complex characteristics of NMHCs involving different extents of contributions from urban vehicular and industrial emissions, local biofuel combustion and biogenic emissions, and biomass burning emissions. At the developed sites, such as Guangzhou in PRD and Lin'an in YRD, vehicular and industrial emissions were the major contributors. However, in rural and remote areas such as at Jiangfeng Mountain on Hainan Island and Tengchong Mountain in southwest of China, long-range transports of biomass burning pollution from the SE Asia subcontinent in addition to contributions from in situ biogenic and other local anthropogenic emissions from South China, are important sources of NMHCs in spring. More in depth studies were conducted in the urban sites of Guangzhou and at the rural site of Dinghu Mountain during 2001 to 2005. The increase in concentration of NMHCs from vehicular and industrial emissions such as ethyne and toluene were more noticeable on Dinghu Mountain than in Guangzhou. The latter even showed decrease levels of toluene, which was contrary to the increase of industrial activities in this region. This was due to the streamlining of urban traffic, upgrading of road networks not only in the urban area but throughout the whole of Guangdong Province, the implementation of stringent emission standards for vehicles as well as polluting industries especially in the urban cities, the relocation of polluting industries from urban to the less developed parts of the PRD and the significant increase in vehicular traffic in the rural areas. We had found for the first time significant increase of propane levels in the urban air of Guangzhou, due to the introduction of LPG-fueled buses and taxis. The signatures of LPG influence were also found in Sanya of Hainan Province, where LPG was used as a fuel in Taxis. The results of this study imply that there are complex emission sources of air pollutant which discharge into the atmosphere from the fast changing urban and rural environments in South China. Hence we observed the rapid changes of NMHC emission patterns. As such, much more research efforts are needed to better understand the impacts of these changes on the atmospheric environment and air quality in this region.