Light attenuation cross-section of black carbon in an urbanatmosphere in northern China

Fine particulate matter (PM2.5) samples were collected over two years in Xi&rsquo;an, China to investigate the relationships between the aerosol composition and the light absorption efficiency of black carbon (BC). Real-time light attenuation of BC at 880&nbsp;nm was measured with an aethalometer. The mass concentrations and elemental carbon (EC) contents of PM2.5 were obtained, and light attenuation cross-sections (&sigma;ATN) of PM2.5 BC were derived. The mass of EC contributed &sim;5% to PM2.5 on average. BC &sigma;ATN exhibited pronounced seasonal variability with values averaging 18.6, 24.2, 16.4, and 26.0&nbsp;m2/g for the spring, summer, autumn, and winter, respectively, while averaging 23.0&nbsp;m2/g overall. &sigma;ATN varied inversely with the ratios of EC/PM2.5, EC/[SO42&minus;], and EC/[NO3&minus;]. This study of the variability in &sigma;ATN illustrates the complexity of the interactions among the aerosol constituents in northern China and documents certain effects of the high EC, dust, sulfate and nitrate loadings on light attenuation.</p

Impact of PM2.5 chemical compositions on aerosol light scattering in Guangzhou - the largest megacity in South China

Daily PM2.5 samples were collected in Guangzhou - the largest megacity in South China, for a period of one month in each season during 2009-2010. Mass concentrations of water-soluble inorganic ions, organic carbon (OC) and elemental carbon (EC) in PM2.5 were determined, and aerosol scattering coefficient (b(sp)) was synchronously measured. The daily PM2.5 mass concentrations ranged from 21.0 to 213.6 mu g m(-3) with an annual average of 76.8 +/- 41.5 mu g m(-3). The highest seasonal average PM2.5 was observed in winter (103.3 +/- 50.1 mu g m(-3)) and the lowest in summer (38.6 +/- 15.7 mu g m(-3)). Annual average PM2.5 mass scattering efficiency (MSE) was 3.5 +/- 0.9 m(2) g(-1), with obvious seasonal variations in sequence of autumn (4.5 +/- 0.2 m(2) g(-1)) &gt; winter (3.9 +/- 0.5 m(2) g(-1)) &gt; spring (3.0 +/- 0.4 m(2) g(-1)) &gt; summer (2.3 +/- 0.3 m(2) g(-1)). To determine the relationship between b and the chemical components of PM2.5, b(sp) was reconstructed in each season using the original IMPROVE formula with a modification of including sea salt aerosols. The estimated bsp using this method was 22 +/- 28% smaller on annual average compared to the measurements. Multiple linear regression of measured b(sp) against (NH4)(2)SO4, NH4NO3, OM (Organic Mass), SS (Sea Salt), FS (Fine Soil), and CM (Coarse Mass) were also performed in all the four seasons. The estimated b(sp) from using the regression equation was 4 +/- 12% larger than the measured values. On average, (NH4)(2)SO4, NH4NO3, OM, SS, FS and CM accounted for 50 +/- 11%, 18 +/- 10%, 19 +/- 5%, 5 +/- 4%, 3 +/- 2% and 5 +/- 6%, respectively, of the estimated b(sp).</p

PM2.5-bound oxygenated PAHs, nitro-PAHs and parent-PAHs from the atmosphere of a Chinese megacity: Seasonal variation, sources and cancer risk assessment

Polycyclic aromatic compounds (PACs) in air particulate matter contribute considerably to the health risk of air pollution. The objectives of this study were to assess the occurrence and variation in concentrations and sources of PM2.5-bound PACs [Oxygenated PAHs (OPAHs), nitro-PAHs and parent-PAHs] sampled from the atmosphere of a typical Chinese megacity (Xi&#39;an), to study the influence of meteorological conditions on PACs and to estimate the lifetime excess cancer risk to the residents of Xi&#39;an (from inhalation of PM2.5-bound PACs). To achieve these objectives, we sampled 24-h PM2.5 aerosols (once in every 6 days, from 5 July 2008 to 8 August 2009) from the atmosphere of Xi&#39;an and measured the concentrations of PACs in them. The PM2.5-bound concentrations of &Sigma;carbonyl-OPAHs, &sum;hydroxyl +carboxyl-OPAHs, &Sigma;nitro-PAHs and &Sigma;alkyl + parent-PAHs ranged between 5&ndash;22, 0.2&ndash;13, 0.3&ndash;7, and 7&ndash;387 ng m&minus;3, respectively, being markedly higher than in most western cities. This represented a range of 0.01&ndash;0.4% and 0.002&ndash;0.06% of the mass of organic C in PM2.5 and the total mass of PM2.5, respectively. The sums of the concentrations of each compound group had winter-to-summer ratios ranging from 3 to 8 and most individual OPAHs and nitro-PAHs had higher concentrations in winter than in summer,suggesting a dominant influence of emissions from household heating and winter meteorological conditions. Ambient temperature, air pressure, and wind speed explained a large part of the temporal variation in PACs concentrations. The lifetime excess cancer risk from inhalation (attributable to selected PAHs and nitro-PAHs) was six fold higher in winter (averaging 1450 persons per million residents of Xi&#39;an) than in summer. Our results call for the development of emission control measures.</p

Characterization and seasonal variations oflevoglucosan in fine particulate matter in Xi’an, China

PM2.5 (particulate matter with an aerodynamic diameter &lt;2.5 mm) samples (n &frac14; 58) collected every sixth day in Xi&rsquo;an, China, from 5 July 2008 to 27 June 2009 are analyzed for levoglucosan (1,6-anhydro-b-D-glucopyranose) to evaluate the impacts of biomass combustion on ambient concentrations. Twenty-four-hour levoglucosan concentrations displayed clear summer minima and winter maxima that ranged from 46 to 1889 ng m 3, with an average of 428 399 ng m 3. Besides agricultural burning, biomass/biofuel combustion for household heating with straws and branches appears to be of regional importance during the heating season in northwestern China. Good correlations (0.70 &lt; R &lt; 0.91) were found between levoglucosan relative to watersoluble K&thorn;, Cl , organic carbon (OC), elemental carbon (EC), and glyoxal. The highest levoglucosan/OC ratio of 2.3% was found in winter, followed by autumn (1.5%). Biomass burning contributed to 5.1&ndash;43.8% of OC (with an average of 17.6 8.4%).</p

Characterization of volatile organic compounds at a roadsideenvironment in Hong Kong: An investigation of influences after airpollution control strategies

Vehicular emission is one of the important anthropogenic pollution sources for volatile organic compounds (VOCs). Four characterization campaigns were conducted at a representative urban roadside environment in Hong Kong between May 2011 and February 2012. Carbon monoxide (CO) and VOCs including methane (CH4), non-methane hydrocarbons (NMHCs), halocarbons, and alkyl nitrates were quantified. Both mixing ratios and compositions of the target VOCs show ignorable seasonal variations. Except CO, liquefied petroleum gas (LPG) tracers of propane, i-butane and n-butane are the three most abundant VOCs, which increased significantly as compared with the data measured at the same location in 2003. Meanwhile, the mixing ratios of diesel- and gasoline tracers such as ethyne, alkenes, aromatics, halogenated, and nitrated hydrocarbons decreased by at least of 37%. The application of advanced multivariate receptor modeling technique of positive matrix factorization (PMF) evidenced that the LPG fuel consumption is the largest pollution source, accounting for 60 ± 5% of the total quantified VOCs at the roadside location. The sum of ozone formation potential (OFP) for the target VOCs was 300.9 μg-O3 m−3, which was 47% lower than the value of 567.3 μg-O3 m−3 measured in 2003. The utilization of LPG as fuel in public transport (i.e., taxis and mini-buses) contributed 51% of the sum of OFP, significantly higher than the contributions from gasoline- (16%) and diesel-fueled (12%) engine emissions. Our results demonstrated the effectiveness of the switch from diesel to LPG-fueled engine for taxis and mini-buses implemented by the Hong Kong Special Administrative Region (HKSAR) Government between the recent ten years, in additional to the execution of substitution to LPG-fueled engine and restrictions of the vehicular emissions in compliance with the updated European emission standards

The Optical Properties of Urban Aerosol in Northern China: A Case Study at Xi’an

Simultaneous measurements of particle scattering coefficient (Bscat) and absorption coefficient (Babs) were conducted at Xi\u27an from mid-August to mid-October 2012 to estimate the particle single scattering albedo (SSA) and the Ångström coefficients in highly polluted urban air. The hourly averaged Bscat was 272 Mm− 1 at 532 nm and 82 Mm− 1 at 870 nm, while hourly averaged Babs was 31 Mm− 1 at 532 nm and 19 Mm− 1 at 870 nm. Similar diurnal variations for Bscat and Babs were observed between the two wavelengths. The averaged SSA was 0.88 at 532 nm and 0.78 at 870 nm. Based on the Ångström coefficients, anthropogenic fine particles show dominant contribution during the sampling period, accompanied by occasional dust events. Moreover, the major contributors to aerosol optical properties are attributed to the mixture of black carbon (BC) and brown carbon (BrC) with non-absorbing components over urban area in northern China. The findings provide useful insights into the factors affecting the visibility in northern Chinese cities and therefore essential knowledge for improving the air quality