Abstract
We analyze 16‐month data of 13 major halocarbons measured at a southern China coastal site in the greater Pearl River Delta (PRD). A total of 188 canister air samples were collected from August 2001 to December 2002. Overall inspection indicated that CH2Cl2, C2Cl4, and C2HCl3 had similar temporal variations while CFC‐11, CFC‐12, and CFC‐113 showed the same emission patterns during the sampling period. Diurnal variations of halocarbons presented different patterns during ozone episode days, mainly related to emission strength, atmospheric dispersion, and photochemical lifetimes. For further statistics and source appointment, Lagrangian backward particle release simulations were conducted to help understand the potential source regions of all samples and classify them into different categories, including local Hong Kong, inner PRD, continental China, and marine air masses. With the exception of HCFC‐142b, the mixing ratios of all halocarbons in marine air were significantly lower than those in urban and regional air (p < 0.01), whereas no significant difference was found between urban Hong Kong and inner PRD regional air, reflecting the dominant impact of the greater PRD regional air on the halocarbon levels. The halocarbon levels in this region were significantly influenced by anthropogenic sources, causing the halocarbon mixing ratios in South China Sea air to be higher than the corresponding background levels, as measured by global surface networks and by airborne missions such as Transport and Chemical Evolution Over the Pacific. Interspecies correlation analysis suggests that CHCl3 is mainly used as a solvent in Hong Kong but mostly as a feedstock for HCFC‐22 in the inner PRD. Furthermore, CH3Cl is often used as a refrigerant and emitted from biomass/biofuel burning in the inner PRD. A positive matrix factorization receptor model was applied to the classified halocarbon samples in the greater PRD for source profiles and apportionments. Seven major sources were identified and quantified. Emissions from solvent use were the most significant source of halocarbons (71 ± 9%), while refrigeration was the second largest contributor (18 ± 2%). By further looking at samples from the inner PRD and from urban Hong Kong separately, we found that more solvent was used in the dry cleaning industry in Hong Kong, whereas the contribution of cleaning solvent in the electronic industry was higher in the inner PRD. Besides the two common sources of solvent use and refrigeration, the contributions of biomass/biofuel burning and feedstock in chemical manufacturing was remarkable in the inner PRD but negligible in Hong Kong. These findings are of help to effectively control and phase out the emissions of halocarbons in the greater PRD region of southern China.
Highlights
[1] We analyze 16-month data of 13 major halocarbons measured at a southern China coastal site in the greater Pearl River Delta (PRD)
[29] Comparing the measurement data in this study to the field campaign in the inner PRD in 2000 [Chan and Chu, 2007], we found that the average mixing ratios for almost all target halocarbons measured in inner PRD and urban Hong Kong fell into the range obtained in 2000 and on the lower side [Chan and Chu, 2007]
[33] In order to obtain a more detailed picture of halocarbons in the study region, we focus on the source profiles and source apportionments of halocarbons in the greater PRD region obtained from the positive matrix factorization (PMF) receptor model
Summary
[2] Halogenated hydrocarbons (halocarbons) are unique air contaminants in the atmosphere, in part because of their persistence. The very low reactivity allows chlorofluorocarbons to survive unchanged in most commercial applications and eventually to be released to the atmosphere in their original gaseous form [Seinfeld and Pandis, 2006] These same CFCs are potentially important greenhouse gases that efficiently absorb infrared radiation [Hofmann et al, 2006]. [6] A comprehensive field measurement campaign was carried out at a polluted rural/coastal site in the PRD from August 2001 to December 2002, in order to understand the photochemical smog problem in this region Using this data set, the causes of a multiday ozone episode were analyzed [Wang and Kwok, 2003], the temporal variability and emission patterns of pollution plumes during October –December 2001 were characterized [Wang et al, 2003], and the seasonal profiles and atmospheric processes of trace gases (including NMHCs) were overviewed [Wang et al, 2005]. The findings extracted in this study are expected to help understand the usage patterns, emissions and controls of halocarbons in the greater PRD region
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