Abstract
Abstract. Using a GC/FID/MS system, we analyzed the mixing ratio of 16 halocarbon species in more than 100 air samples collected in 2004 from the Pearl River Delta (PRD) region of southern China. The results revealed that there are elevated mixing ratios for most of halocarbons, especially for HClC = CCl2 (trichloroethylene, TCE), CH2Cl2 (dichloromethane, DCM), CH3 Br (bromomethane), HCFC-22, CHCl3 (trichloromethane), CCl4 (tetrachloromethane), Cl2C = CCl2 (perchloroethylene, PCE), CH3CCl3 (methyl chloroform, MCF), and CFC-12. Comparisons were done with the data from TRACE-P and ALE/GAGE/AGAGE experiments, we found that the large variability in mixing ratios (relative standard deviation ranged from 9.31 % to 96.55 %) of the halocarbons suggested substantial local emissions from the PRD region in 2004. Correlations between the mixing ratio of each species and carbon monoxide (CO) was examined, and then the emission of each halocarbon was quantified based on scaling the optimized CO emission inventory with the slope of the regression line fitted to each species relative to CO. The calculated results revealed that mass of CH2Cl2 (7.0 Gg), CH3CCl3 (6.7 Gg), and Cl2C = CCl2 (2.3 Gg) accounted for about 62.9 % of total halocarbon emissions, it suggested a significant contribution from solvent use in the PRD region. Emissions of HCFC-22 (3.5 Gg), an alternative refrigerant to chlorofluorocarbons (CFCs), were about 2.3 times greater than those of CFC-12 (1.6 Gg). CFC-12 and HCFC-22 accounted for 21.5 % of total emissions of halocarbons, so that the refrigerant would be the second largest source of halocarbons. However, the ratio approach found only minor emissions of CFCs, such as CFC-11, and the emission of CFC-114 and CFC-113 were close to zero. Emissions of other anthropogenic halocarbons, such as CCl4, CHCl3, CH3Br, and CH3Cl, were also estimated. Where possible, the emissions estimated from the measured ratios were compared with results from source inventory techniques, we found that both approaches gave emissions at similar magnitude for most of the halocarbons, except CFC-11. The comparison suggested that the ratio method may be a useful tool for assessing regional halocarbon emissions, and emission uncertainty could be further reduced by incorporating both longer-term and higher-frequency observations, as well as improving the accuracy of the CO inventory.
Highlights
The importance of halocarbons in the atmosphere has been recognized since the 1970s, when Lovelock measured out the ambient concentrations of chlorofluorocarbons (CFCs) using a gas chromatogram coupled with electron capture detector
The 16 halocarbons measured by GC-FID/MS, coupled with a cryogenic pre-concentrator system, were: CFC-11, CFC-12, CFC113, CFC-114, HCFC-22, CH3CCl3, CCl4, CHCl3, CH2Cl2, CH3Cl, CH3Br, CCl2 = CCl2, CHCl = CCl2, CHCl2CH2Cl, CH3CH2Cl, and CH3CHClCH2Cl
Comparing to the mixing ratio obtained from TRACEP and ALE/GAGE/AGAGE, the statistical results given in both Tables 1 and 2 showed that the regional mixing ratios of most halocarbons were elevated for their mixing ratios in Pearl River Delta (PRD) region, especially for HClC = CCl2, CH2Cl2, CH3Br, HCFC-22, CHCl3, CCl4, Cl2C = CCl2, CH3CCl3, and CFC12
Summary
The importance of halocarbons in the atmosphere has been recognized since the 1970s, when Lovelock measured out the ambient concentrations of chlorofluorocarbons (CFCs) using a gas chromatogram coupled with electron capture detector. As a subclass of volatile organic compounds, halocarbons play an important role in the destruction of stratospheric ozone, some of them function as the potential greenhouse gases. Both of the two effects have propelled halocarbons to the forefront of atmospheric chemistry research. Environmental agencies in many countries have prepared national emissions inventories of halocarbons, and these statistical emissions estimates were used to help to accelerate the halocarbon phase-out. These emissions inventories were relied primarily on bottom-up approaches, and compiled based on production, end-use and the time schedule data. Uncertainties arise if the production figures do not cover all manufacturers
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