Volatile organic compounds (VOCs) emitted from both biogenic and anthropogenic sources play very important roles in the tropospheric chemistry. In the atmosphere, their degradation can form a series of harmful secondary pollutants. To develop effective control measures for the secondary pollutants, the concentrations and sources of VOCs is needed to study. In this study, we developed a Liquid Nitrogen-free/ capillary columns system to research C2-C12 NMHCs in the atmosphere. In addition, volatile organic compounds emitted from conjugated-domestic coal combustion and the atmospheric VOCs in North China Plain during the summertime were sampled to thoroughly investigate their characterestics; and also the sensitive chemistry of ozone formation in city and rural area of North China Plain during the summertime were studied.
1. A LN2-free GC-FID system (equipped with three capillary columns) has been developed for measuring atmospheric C2-C12 hydrocarbons. The LN2-free GC-FID system is consisted of a sampling unit (3mm I.D. stainless tube), a cooling unit (two cooler) and three separation units. The cooling unit which included two cooler head is used to meet the low temperature needs of the sampling unit (SS tube) and the separation unit (capillary column). The sampling unit includes a pump, a Nafion-dehydration tube, a mass flower controller (MFC) and a stainless tube. The separation unit attached on the cooling column, and OV-1 column (30 m × 0.32 mm I.D.) and PLOT column (10m× 0.32 mm I.D.) were used to separate the C2-C12 hydrocarbons. The program temperature of the OV-1 amd PLOT columns were achieved to separate C2-C12 NMHCs. The signals of hydrocarbons obtained by VOCs analyzer and the enrichment amount of hydrocarbons had good linear correlations.
2. Volatile organic compounds (VOCs) emitted from a prevailing domestic stove and new conjugated domestic stove were studied. In the traditional stove, the concentrations of the VOCs quickly increased after the coal loading and achieved their peak values in a few minutes. Whereas, only low concentrations of VOCs were found at the beginning of the burning processes in the conjugated dometstic stove. Alkanes (46.57-48.13%) accounted for the largest proportion under the combustion, followed by aromatics, alkenes, acetylene and branched alkanes. The emission factors of the total VOCs from the traditional domestic stove were nearly one magnitude greater than those from conjugated domestic stove.
3. Atmospheric non-methane hydrocarbon compounds (NMHCs) were measured at sampling site in rural area of North Plain to recognize their variation characteristics, pollution levels and the O3 formation sensitivity. The proportions of alkanes, alkenes, aromatics and acetylene to the total NMHCs were 57.72%, 15.74%, 17.67% and 8.87%, respectively. Ethane were the most abundant species. The peak concentrations of ozone and TNMHCs/NOx ratio at the rural site in diurnal profiles both appeared in the period from 11:00 am to 15:00 pm. The average TNMHCs/NOx ratio was greater than 8 during the daytime and thus proved that the ozone generation in this period was limited by NOx. Isoprene was the largest contributor with the TNMHCs < 20 ppbv, and the contribution of isoprene gradually decreased to approximately 10% under TNMHCs > 30 ppbv, whereas the change of the contributions of alkanes, alkenes and aromatics showed the opposite trend. The order of the contribution of NMHC groups to the OFP was aromatics > alkenes > alkanes > isoprene > acetylene.
4. Atmospheric volatile organic compounds (VOCs) were measured at sampling sites in Daxing district of Beijing to recognize their pollution levels, variation characteristics and the O3 formation sensitivity. Dibromochloromethane, ethane,nonane, chloroform and toluene were found to be the top five VOCs during the summertime. The proportions order of VOCs was: halohydrocarbons > alkanes >aromatics > ovocs > alkenes > acetylene. Based on the results of the typical ratio and EKMA, the ozone generation in this cite was limited by VOCs. For the atmospheric VOCs in Beijing during the summertime, five emission sources were obtained by positive matrix factorization (PMF), including gasoline exhaust, biogenic, solvent evaportaion, desiel exhaust and painting and printing. Solvent evaportaion and desiel exhaust were found to make the greatest contribution (20.7~32.1%) to atmospheric NMHCs. The propotions of the five emission sources identified by PMF to O3 formation were 26.9 4.1%(diesel exhaust),24.4 8.5% (biogenic), 19.5 6.5% (painting and printing), 16.7 2.5% (solvent evaporation) and 12.6 1.5% (gasoline exhaust), respectively.