Radiocarbon (C-14) has become a powerful tracer in source apportionments of atmospheric carbonaceous particles. Fine particles (PM2.5) were collected at a rural site of Beijing in the summer and winter of 2007. The fractions of contemporary carbon (f(C)) in total carbon (TC) and elemental carbon (EC) are presented using C-14 measurements. This value directly represents the contemporary biogenic contribution, since recently living biomass and biogenic organic compound emissions have f(C) = 1, whereas anthropogenic emissions from fossil carbon have f(C) = 0 because the C-14 in the latter has completely decayed. The measured f(C) (TC) values range from 0.30 to 0.38 (n = 12) in winter and 0.31 to 0.44 (n = 12) in summer, respectively. The levels of f(C) values are lower than those from other rural sites in the world, indicating that the Yufa site was heavily influenced by anthropogenic emissions. The high TC concentrations in winter with the lower average f(C) (TC) suggest that coal burning for residential heating was significant contributors to the TC concentrations. The sources of contemporary carbon are primary emissions due to biomass burning, and biogenic secondary organic aerosol. Biomass burning was a dominant contributor in the winter. Fossil fuels represented 80-87% of EC in both seasons. (C) 2012 Elsevier Ltd. All rights reserved.

Both organic carbon (OC) and elemental carbon (EC) were measured during PRIDE-PRD 2006 summer campaign by using a semi-continuous thermal-optical carbon analyzer at a rural site, Back Garden (BG), which is located 50 km to the northwest of Guangzhou City. Together with the online EC/OC analyzer, various kinds of instruments related to aerosol chemical properties were employed here, which provided a good opportunity to check data quality. The concentrations of OC correlated well with the mass of organic matter (OM) and water soluble organic carbon (WSOC), implying the reliability of the data measured in this campaign. The average OC concentrations in fine particle for three typical periods during the campaign (local emission influence, typhoon and precipitation and normal days) were 28.1 mu gC m(-3), 4.0 mu gC m(-3) and 5.7 mu gC m(-3), respectively; and EC were 11.6 mu gC m(-3), 1.8 mu gC m(-3), and 3.3 mu gC m(-3), respectively. The diurnal patterns of EC and OC during the campaign were higher at night and in early morning than daytime, which was probably caused by the primary emission and accumulation in the occurrence of low boundary layer. Compared with the constant diurnal enhancement ratios of EC, the enhancement ratio of OC (OC versus (CO-CObackground)) kept in a relative high level in the afternoon, with a similar diurnal profile to oxygenated organic aerosol (OOA), due to the strong photochemical formation of OC. Here, a modified EC tracer method was used to estimate the formation of secondary organic carbon (SOC). These results showed that the average SOC concentration (normal days) at BG site was about 2.0 +/- 2.3 mu gC m(-3), and the SOC fraction in OC could reach up to 80% with the average of 47 %. The modified approach in this study proved to be effective and reliable for SOC estimation based on good correlations between estimated SOC versus OOA or WSOC, and estimated POC versus hydrocarbon-like organic aerosol (HOA).

Simultaneous measurements of aerosol size, distribution of number, mass, and chemical compositions were conducted in the winter of 2007 in Beijing using a Twin Differential Mobility Particle Sizer and a Micro Orifice Uniform Deposit Impactor. Both material density and effective density of ambient particles were estimated to be 1.61 +/- 0.13 g cm(-3) and 1.62 +/- 0.38 g cm(-3) for PM1.8 and 1.73 +/- 0.14 g cm(-3) and 1.67 +/- 0.37 g cm(-3) for PM10. Effective density decreased in the nighttime, indicating the primary particles emission from coal burning influenced the density of ambient particles. Size-resolved material density and effective density showed that both values increased with diameter from about 1.5 g cm(-3) at the size of 0.1 mu m to above 2.0 g cm(-3) in the coarse mode. Material density was significantly higher for particles between 0.56 and 1.8 mu m during clean episodes. Dynamic Shape Factors varied within the range of 0.95-1.13 and decreased with particle size, indicating that coagulation and atmospheric aging processes may change the shape of particles.

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 alpha-pinene, and 2.3 +/- 1.7% from beta-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, alpha-pinene, and beta-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 (similar to 2 mu g 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.