Ambient aerosol samples were collected at an urban site and an upwind rural site of Beijing during the CAREBEIJING-2008 (Campaigns of Air quality REsearch in BEIJING and surrounding region) summer field campaign. Contributions of primary particles and secondary organic aerosols (SOA) were estimated by chemical mass balance (CMB) modeling and tracer-yield method. The apportioned primary and secondary sources explain 73.8% ± 9.7% and 79.6% ± 10.1% of the measured OC at the urban and rural sites, respectively. Secondary organic carbon (SOC) contributes to 32.5 ± 15.9% of the organic carbon (OC) at the urban site, with 17.4 ± 7.6% from toluene, 9.7 ± 5.4% from isoprene, 5.1 ± 2.0% from α-pinene, and 2.3 ± 1.7% from β-caryophyllene. At the rural site, the secondary sources are responsible for 38.4 ± 14.4% of the OC, with the contributions of 17.3 ± 6.9%, 13.9 ± 9.1%, 5.6 ± 1.9%, and 1.7 ± 1.0% from toluene, isoprene, α-pinene, and β-caryophyllene, respectively. Compared with other regions in the world, SOA in Beijing is less aged, but the concentrations are much higher; between the sites, SOA is more aged and affected by regional transport at the urban site. The high SOA loading in Beijing is probably attributed to the high regional SOC background (~2 μg m(-3)). The toluene SOC concentration is high and comparable at the two sites, implying that some anthropogenic components, at least toluene SOA, are widespread in Beijing and represents a major factor in affecting the regional air quality. The aerosol gaseous precursor concentrations and temperature correlate well with SOA, both affecting SOA formation. The significant SOA enhancement with increasing water uptake and acidification indicates that the aqueous-phase reactions are largely responsible SOA formation in Beijing.
Elevated ground-level ozone (O 3 ), reflecting atmospheric oxidative capacity, are of increasing concern. High levels of total oxidants (O x = O 3 + NO 2 ) have been persistently observed as a feature of Beijing's air pollution. Beijing is a well-known megacity requiring the enforcement of stringent air quality controls as rapid economic growth continues. To evaluate the effect of air quality controls in recent years, ground-based on-line measurements at an urban site were conducted in summer and the variations in O 3 with simultaneous changes in NO x and volatile organic compounds (VOCs) between 2005 and 2011 were analyzed. Both NO x and total VOCs in Beijing decreased over the study period, 1.4 ppbv yr −1 and 1.6 ppbv yr −1 , respectively. However, VOCs reactivity, in terms of OH loss rate, showed an indistinct statistical trend due to unsteady variations from naturally emitted isoprene, though some anthropogenic species showed decreasing trends, such as pentane, benzene and toluene. Meanwhile, daytime average O 3 increased rapidly at an annual rate of 2.6 ppbv yr −1 , around 5 % yr −1 between 2005 and 2011. Considering the influence of NO titration effect and elevated regional ozone background in the North China Plain (NCP), the main reason for such an increase in oxidants was subject to "local" photochemistry. A simplified model was used to evaluate the effect of changes in the levels of ozone precursors on ozone production. We found that between 2001 and 2006, the production rate of total oxidants, P (O x ) increased rapidly due to increased VOC levels and decreasing NO 2 , while from 2006 to 2011 P (O x ) re-mained high, though decreased slightly as a consequence of the decrease in both VOC reactivity (−5 % yr −1 ) and NO x (−4 % yr −1 ). Observations have shown that Beijing's efforts to control air pollution were somehow effective in cutting ozone precursors, but still left higher ground-level ozone. We surmised that it resulted from potential contributions from OVOCs and regional transport near Beijing. Therefore, Beijing needs deeper cooperation with adjacent provinces to control ozone pollution together. To impel this kind of joint prevention and control program, ground-level ozone should become a mandatory index for air quality management, and a faster reduction of VOCs, especially reactive VOCs, in urban areas, should coordinate with national NO x emission control programs.
Abstract. We measured levels of ambient volatile organic compounds (VOCs) at seven sites in the Pearl River Delta (PRD) region of China during the Air Quality Monitoring Campaign spanning 4 October to 3 November 2004. Two of the sites, Guangzhou (GZ) and Xinken (XK), were intensive sites at which we collected multiple daily canister samples. The observations reported here provide a look at the VOC distribution, speciation, and photochemical implications in the PRD region. Alkanes constituted the largest percentage (>40%) in mixing ratios of the quantified VOCs at six sites; the exception was one major industrial site that was dominated by aromatics (about 52%). Highly elevated VOC levels occurred at GZ during two pollution episodes; however, the chemical composition of VOCs did not exhibit noticeable changes during these episodes. We calculated the OH loss rate to estimate the chemical reactivity of all VOCs. Of the anthropogenic VOCs, alkenes played a predominant role in VOC reactivity at GZ, whereas the contributions of reactive aromatics were more important at XK. Our preliminary analysis of the VOC correlations suggests that the ambient VOCs at GZ came directly from local sources (i.e., automobiles); those at XK were influenced by both local emissions and transportation of air mass from upwind areas.
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