Aromatic hydrocarbons as ozone precursors before and after outbreak of the 2008 financial crisis in the Pearl River Delta region, south China

Abstract

[1] In the second half of 2008 China's highly industrialized Pearl River Delta (PRD) region was hard-hit by the financial crisis (FC). This study reports volatile organic compounds measured in the PRD during November-December in both 2007 before the FC and 2008 after the FC. While total mixing ratios of non-methane hydrocarbons (NMHCs) on average were only about 7% lower from 40.2 ppbv in 2007 to 37.5 ppbv in 2008, their ozone formation potentials (OFPs) dropped about 30%, resulting from about 55% plummet of aromatic hydrocarbons (AHs) against a greater than 20% increase of total alkanes/alkenes. The elevated alkanes and alkenes in 2008 could be explained by greater emissions from vehicle exhausts and LPG combustion due to rapid increase of vehicle numbers and LPG consumption; the drop of AHs could be explained by reduced emissions from industries using AH-containing solvents due to the influence of the FC, as indicated by much lower ratios of toluene to benzene and of xylenes/trichloroethylene/ tetrachloroethylene to carbon monoxide (CO) in 2008. Source apportionment by positive matrix factorization (PMF) also revealed much less contribution of industry solvents to total anthropogenic NMHCs and particularly to toluene and xylenes in 2008 than in 2007. Based on PMF reconstructed source contributions, calculated OFPs by industrial emissions were responsible for 40.8% in 2007 in contrast to 18.4% in 2008. Further investigation into local industry output statistics suggested that the plummet of AHs in 2008 should be attributed to small enterprises, which contributed largely to ambient AHs due to their huge numbers and non-existent emission treatment, but were much more influenced by the FC.

Source attributions of hazardous aromatic hydrocarbons in urban, suburban and rural areas in the Pearl River Delta (PRD) region

“…Detailed cryogenically concentration steps are described elsewhere [26,48]. Briefly, VOCs inside the canisters were initially concentrated using liquid-nitrogen cryogenic trap at −160 • C. The trapped VOCs were then transferred by pure helium to a secondary trap at −40 • C with Tenax-TA as adsorbent.…”

“…Benzene, as a carcinogenic compound forbidden to be used in industry, were mainly from automobile exhausts in urban areas [5,24,64], so dominant contribution from vehicle exhausts in the urban site GEMC explained the higher benzene/acetylene ratio than at other sites [5,28]. As toluene, C 8 -aromatics and C 9 -aromatics were widely used as solvents in painting, coating, printing and cleaning processes in the highly industrialized PRD region [3,26,33,67], their high ratios to acetylene at WQS suggested substantial contribution of AHs from industrial emissions in the upwind city of Dongguan, a worldknown manufacturing center in the region. Moreover, the ratios of toluene, C 8 -aromatics and C 9 -aromatics to acetylene at WQS were 1.24 ± 0.13, 0.68 ± 0.07 and 0.20 ± 0.03, consistent with ratios of 1.19, 0.68 and 0.22 previously reported in Dongguan, respectively [5], indicating substantial impacts of emissions from Dongguan on air pollutants occurring at WQS during fall-winter with northeast prevailing winds.…”

“…In the PRD region, the rapid growth in economy has resulted in fast increase in anthropogenic emissions of air pollutants [21], and as an important class of anthropogenic volatile organic compounds (VOCs), AHs were found to have comparatively higher ambient levels [3,5,[22][23][24][25][26] with tremendous impacts on air quality in the region. Studies showed that in the PRD region ozone formation was largely VOC-limited with AHs among the most important precursors [26][27][28][29], and AHs alone were responsible for over 75% secondary organic carbon in fine particles [20].…”

“…Studies showed that in the PRD region ozone formation was largely VOC-limited with AHs among the most important precursors [26][27][28][29], and AHs alone were responsible for over 75% secondary organic carbon in fine particles [20]. Therefore, emission control of AHs is vital to lower regional ozone pollution and SOA in the region.…”

Changes in visibility with PM2.5 composition and relative humidity at a background site in the Pearl River Delta region

“…Nonetheless, site specific properties, size distribution and chemical composition of aerosols are vital factors behind this discrepancy. It is worth noting that taking all chloride as SS-related will overestimate SS, since short-lived chlorinated hydrocarbons were present, which were widely used in China's highly industrialized PRD region (Zhang et al, 2012b), and their degradation in the ambient will also be a source of chloride detected in this study.…”