Brown Carbon Aerosol in Urban Xi’an, Northwest China: TheComposition and Light Absorption Properties

Light-absorbing organic carbon (i.e., brown carbon or BrC) in the atmospheric aerosol has significant contribution to light absorption and radiative forcing. However, the link between BrC optical properties and chemical composition remains poorly constrained. In this study, we combine spectrophotometric measurements and chemical analyses of BrC samples collected from July 2008 to June 2009 in urban Xi'an, Northwest China. Elevated BrC was observed in winter (5 times higher than in summer), largely due to increased emissions from wintertime domestic biomass burning. The light absorption coefficient of methanol-soluble BrC at 365 nm (on average approximately twice that of water-soluble BrC) was found to correlate strongly with both parent polycyclic aromatic hydrocarbons (parent-PAHs, 27 species) and their carbonyl oxygenated derivatives (carbonyl-OPAHs, 15 species) in all seasons (r(2) > 0.61). These measured parent-PAHs and carbonyl-OPAHs account for on average similar to 1.7% of the overall absorption of methanol-soluble BrC, about 5 times higher than their mass fraction in total organic carbon (OC, similar to 0.35%). The fractional solar absorption by BrC relative to element carbon (EC) in the ultraviolet range (300-400 nm) is significant during winter (42 +/- 18% for water-soluble BrC and 76 +/- 29% for methanol-soluble BrC), which may greatly affect the radiative balance and tropospheric photochemistry and therefore the climate and air quality

Primary PM2.5 and trace gas emissions from residential coal combustion: assessing semi-coke briquette for emission reduction in the Beijing-Tianjin-Hebei region, China

In response to severe haze pollution, the Chinese State Council set PM2.5 improvement targets for the Beijing-Tianjin-Hebei (BTH) region in 2013. To achieve the targets for the residential sector, semi-coke briquettes are being considered as a replacement for traditional raw coals with the help of financial subsidy, but information on the emission from them and the impacts on the air quality is limited. Laboratory experiments were conducted to determine emission factors (EFs) for a typical semi-coke briquette, its parent material (bituminous raw-coal-chunk) and three types of traditional coals (bituminous raw-coal-chunk, anthracite raw-coal-chunk and anthracite coal-briquette) extensively used in BTH. Compared with the parent material, significant lower EFs of primary PM2.5, organic carbon (OC), element carbon (EC), the sum of 16 polycyclic aromatic hydrocarbon components (PAHs), SO42−, NO3−, hazardous trace elements (HTEs) and NOx were found in semi-coke briquette. A scenario for the BTH region in 2015 in which raw coals were replaced with the semi-coke briquette showed that amounts of pollutants emitted from residential coal combustion could decrease by 91.6% for primary PM2.5, 94.0% for OC, 99.6% for EC, 99.9% for PAHs, 94.2% for NO3−, 45.6% for HTEs, 70.9% for NOx and 22.3% for SO2. However, SO42− loadings evidently would increase if raw coals were replaced with either semi-coke briquette or anthracite coal-briquette. Geographic distributions of modeled reductions were developed to identify emission-reducing hot-spots and aid in the development of clean energy policies. Replacement of traditional raw coals with the semi-coke briquette apparently could lead to significant environmental improvements in BTH and other regions in China

Characterization of the chemical components and bioreactivity of fine particulate matter produced during crop-residue burning in China

Five types of crop residue (rice, wheat, corn, sorghum, and sugarcane) collected from different provinces in China were used to characterize the chemical components and bioreactivity properties of fine particulate matter (PM2.5) emissions during open-burning scenarios. Organic carbon (OC) and elemental carbon (EC) were the most abundant components, contributing 41.7%-54.9% of PM2.5 emissions. The OC/EC ratio ranged from 8.8 to 31.2, indicating that organic matter was the dominant component of emissions. Potassium and chloride were the most abundant components in the portion of PM2.5 composed of water-soluble ions. The coefficient of divergence ranged from 0.27 to 0.51 among various emissions profiles. All samples exposed to a high PM2.5 concentration (150 mu g/mL) exhibited a significant reduction in cell viability (A549 lung alveolar epithelial cells) and increase in lactic dehydrogenase (LDH) and interleukin 6 levels compared with those exposed to 20 or 0 mu g/mL Higher bioreactivity (determined according to LDH and interleukin 6 level) was observed for the rice, wheat, and corn samples than for the sorghum straw samples. Pearson's correlation analysis suggested that OC, heavy metals (chromium, manganese, iron, nickel, copper, zinc, tin, and barium), and water-soluble ions (fluoride, calcium, and sulfate) are the components potentially associated with LDH production

Occurrence, gas/particle partitioning and carcinogenic risk of polycyclicaromatic hydrocarbons and their oxygen and nitrogen containingderivatives in Xi'an, central China

29 parent- and alkyl-polycyclic aromatic hydrocarbons (PAHs), 15 oxygenated-PAHs (OPAHs), 11 nitrated-PAHs (NPAHs) and 4 azaarenes (AZAs) in both the gaseous and particulate phases, as well as the particulate-bound carbon fractions (organic carbon, elemental carbon, char, and soot) in ambient air sampled in March and September 2012 from an urban site in Xi&#39;an, central China were extracted and analyzed. The average concentrations (gaseous&nbsp;+&nbsp;particulate) of &sum;&nbsp;29PAHs, &sum;&nbsp;15OPAHs, &sum;&nbsp;11NPAHs and &sum;&nbsp;4AZAs were 1267.0&nbsp;&plusmn;&nbsp;307.5, 113.8&nbsp;&plusmn;&nbsp;46.1, 11.8&nbsp;&plusmn;&nbsp;4.8 and 26.5&nbsp;&plusmn;&nbsp;11.8&nbsp;ng&nbsp;m&minus;&nbsp;3 in March and 784.7&nbsp;&plusmn;&nbsp;165.1, 67.2&nbsp;&plusmn;&nbsp;9.8, 9.0&nbsp;&plusmn;&nbsp;1.5 and 21.6&nbsp;&plusmn;&nbsp;5.1&nbsp;ng&nbsp;m&minus;&nbsp;3 in September, respectively. Concentrations of &sum;&nbsp;29PAHs, &sum;&nbsp;15OPAHs and &sum;&nbsp;11NPAHs in particulates were significantly correlated with those of the carbon fractions (OC, EC, char and soot). Both absorption into organic matter in particles and adsorption onto the surface of particles were important for PAHs and OPAHs in both sampling periods, with more absorption occurring in September, while absorption was always the most important process for NPAHs. The total carcinogenic risk of PAHs plus the NPAHs was higher in March. Gaseous compounds, which were not considered in most previous studies, contributed 29 to 44% of the total health risk in March and September, respectively.</p

Stable carbon isotopes and levoglucosan for PM2.5 elemental carbon sourceapportionments in the largest city of Northwest China

Stable carbon isotopes provide information on aerosol sources, but no extensive long-term studies of these isotopes have been conducted in China, and they have mainly been used for qualitative rather than quantitative purposes. Here, 24 h PM2.5 samples (n = 58) were collected from July 2008 to June 2009 at Xi&#39;an, China. The concentrations of organic and elemental carbon (OC and EC), water-soluble OC, and the stable carbon isotope abundances of OC and EC were determined. In spring, summer, autumn and winter, the mean stable carbon isotope in OC (&delta;13COC) were &minus;26.4 &plusmn; 0.6, &minus;25.8 &plusmn; 0.7, &minus;25.0 &plusmn; 0.6 and &minus;24.4 &plusmn; 0.8&permil;, respectively, and the corresponding &delta;13CEC values were &minus;25.5 &plusmn; 0.4, &minus;25.5 &plusmn; 0.8, &minus;25.2 &plusmn; 0.7 and &minus;23.7 &plusmn; 0.6&permil;. Large &delta;13CEC and &delta;13COC values in winter can be linked to the burning coal for residential heating. Less biomass is burned during spring and summer than winter or fall (manifested in the levels of levoglucosan, i.e., 178, 85, 370, 935 ng m&minus;3 in spring, summer, autumn, and winter), and the more negative &delta;13COC in the warmer months can be explained by the formation of secondary organic aerosols. A levoglucosan tracer method combined with an isotope mass balance analysis indicated that biomass burning accounted for 1.6&ndash;29.0% of the EC, and the mean value in winter (14.9 &plusmn; 7.5%) was 7 times higher than summer (2.1 &plusmn; 0.4%), with intermediate values of 6.1 &plusmn; 5.6 and 4.5 &plusmn; 2.4% in autumn and spring. Coal combustion accounted for 45.9 &plusmn; 23.1% of the EC overall, and the percentages were 63.0, 37.2, 36.7, and 33.7% in winter, autumn, summer and spring respectively. Motor vehicles accounted for 46.6 &plusmn; 26.5% of the annual EC, and these contributed over half (56.7&ndash;61.8%) of the EC in all seasons except winter. Correlations between motor vehicle-EC and coal combustion-EC with established source indicators (B(ghi)P and As) support the source apportionment results. This paper describes a simple and accurate method for apportioning the sources of EC, and the results may be beneficial for developing model simulations as well as controlling strategies in future

Black carbon aerosol in winter northeastern Qinghai–TibetanPlateau, China: the source, mixing state and optical property

Black carbon (BC) aerosol at high altitudes of the Qinghai-Tibetan Plateau has potential effects on the regional climate and hydrological cycle. An intensive measurement campaign was conducted at Qinghai Lake (~3200m above sea level) at the edge of the northeastern Qinghai- Tibetan Plateau during winter using a ground-based single particle soot photometer (SP2) and a photoacoustic extinctiometer (PAX). The average concentration of refractory BC (rBC) and number fraction of coated rBC were found to be 160&Acirc;&plusmn;190 ngm-3 and 59% for the entire campaign, respectively. Significant enhancements of rBC loadings and number fraction of coated rBC were observed during a pollution episode, with an average value of 390 ngm-3 and 65%, respectively. The mass size distribution of rBC particles showed log-normal distribution, with a peak diameter of ~187 nm regardless of the pollution level. Five-day backward trajectory analysis suggests that the air masses from north India contributed to the increased rBC loadings during the campaign. The potential source contribution function (PSCF) model combined with the fire counts map further proves that biomass burning from north India is an important potential source influencing the northeastern Qinghai-Tibetan Plateau during the pollution episode. The rBC mass absorption cross section (MACrBC/ at &Icirc;&raquo; = 532 nm was slightly larger in clean days (14.9m&Acirc;&sup2; g-1) than during the pollution episode (9.3m&Acirc;&sup2; g-1), likely due to the effects of brown carbon and the uncertainty of the MACrBC calculation. The MACrBC was positively correlated with number fraction of coated rBC during the pollution episode with an increasing rate of 0.18 (m&Acirc;&sup2; g-1)%-1. The number fraction of coated rBC particles showed positive correlation with light absorption, suggesting that the increase of coated rBC particles will enhance the light absorption. Compared to rBC mass concentration, rBC mixing sate is more important in determining absorption during the pollution episode, estimated from the same percentage-wise increment of either rBC mass concentration or the number fraction of coated rBC. The estimated BC direct radiative forcing was C0.93Wm-2 for the pollution episode, which is 2 times larger than that in clean days. Our study provides insight into the potential climatic impacts of rBC aerosol transported to the Qinghai-Tibetan Plateau from south Asian regions, and is also useful for future modeling studies.</p

Emission Characteristics of Primary Brown Carbon Absorption From Biomass and Coal Burning: Development of an Optical Emission Inventory for China

Brown carbon (BrC) affects the Earth's radiative balance due to its strong light absorption at short wavelengths. A custom-made combustion chamber was used to simulate biomass and coal burning and to investigate the emission characteristics of BrC absorption. Absorption angstrom ngstrom exponents (AAEs) at the wavelength pair of 370 and 880nm ranged from 1.19 to 3.25, suggesting the possible existence of BrC in biomass- and coal-burning emissions. Based on the assumption that AAE(BC)=1.0, BrC from biomass burning contributed to 41-85% of the total particles light absorption at 370nm, which is much higher than that from coal burning (15-18%). The estimated absorption emission factors of BrC at 370nm for biomass and coal burning were 15-47 and 2-13m(2)/kg, respectively. A 10x10km gridded BrC optical emission inventory for biomass and coal burning in China for 2015 was developed based on the measured absorption emission factors of BrC values and high-resolution activity data. The total annual BrC absorption cross section emissions from biomass and residential coal burning were 4,194Gm(2) (relative uncertainty at the 95% confidence level of -33.2, 41.2%) and 615Gm(2) (-39.3, 40.1%), respectively. These results should be useful for improving estimates of the radiative effects of BrC in China

A Biomass Combustion Chamber: Design, Evaluation, and a Case Study of WheatStraw Combustion Emission Tests

Open biomass burning is a significant source of trace gases and particulate pollutants on a global scale and plays an important role in both atmospheric chemistry and climate change. To study the emission characteristics of biomass burning, with a focus on crop residue combustion in Northwest China, a combustion chamber was established. This paper describes the design, structure, and operating principles of the chamber. A series of evaluation tests were conducted, demonstrating its applicability in emission studies. The combustion chamber was equipped with a thermoanemometer and a dilution sampler as well as multiple sampling ports for interfacing with different monitors. A case study of wheat straw combustion was performed to demonstrate reproducibility and comparability of the derived emission factors with prior studies. The combustion chamber may be applied to develop emission factors to update emission inventories and source profiles for improving source apportionment.</p

Emission Characteristics of Carbonaceous Particles and Trace Gases from Open Burning of Crop Residues in China

Open burning of crop residue is an important source of carbonaceous pollutants, and has a large impact on the regional environment and global climate change. Laboratory burn tests were conducted using a custom-made combustion chamber to determine pollutants (i.e. CO2, CO, PM2.5, organic carbon (OC) and elemental carbon (EC)) emission factors (EFs) of wheat straw, rice straw and corn stalk; the three major agricultural crop residues in China. The average EFs were estimated to be 1351 ± 147 g kg−1 for CO2, 52.0 ± 18.9 g kg−1 for CO, 10.6 ± 5.6 g kg−1 for PM2.5, 4.8 ± 3.1 g kg−1 for OC and 0.24 ± 0.12 g kg−1 for EC. In addition, the effect of fuel moisture was investigated through the controlled burning of wheat straw. Increasing the moisture content decreased the CO2 EF, and increased the EFs of CO, PM2.5 and OC. Based on measurements from this study and nationwide statistics in crop type and area, pollutants emission inventories for crop residue combustion with 1° × 1° resolution were compiled for 2008. Total emissions were 120 Tg CO2, 4.6 Tg CO, 0.88 Tg PM2.5, 0.39 Tg OC and 0.02 Tg EC

Physicochemical characteristics of black carbonaerosol and its radiative impact in a pollutedurban area of China

Black carbon (BC) aerosol plays an important role in the Earth&rsquo;s radiative balance. An intensive measurement campaign was conducted at Xi&rsquo;an, China, from December 2012 to January 2013 to investigate the sources and physicochemical characteristics of refractory BC (rBC) and its direct radiative forcing at the surface. The overall average rBC concentration for the campaign was 8.0 &plusmn; 7.1 &mu;g m 3. Source apportionment based on positive matrix factorization showed that traffic was the dominant rBC source (46.0%), followed by coal burning (33.9%) and biomass burning (20.1%). The rBC mass size distributions were monomodal and lognormal with larger mass median diameters for coal burning source (215 nm) compared with the traffic source (189 nm). Coal burning rBC was more strongly associated with sulfate than traffic rBC, suggesting a higher cloud condensation nuclei activity. The slope of a robust linear regression between rBC and carbon monoxide (CO) for all samples was 5.9 &mu;g m 3 ppm 1, and the slope for the coal burning source (4.5 &mu;g m 3 ppm 1) was larger than that for the traffic source (2.7 &mu;g m 3 ppm 1). The net rBC emission during winter of 2009 was estimated to be 4.5 Gg based on the relationship between rBC and CO. A Tropospheric Ultraviolet and Visible radiation model showed that the average daytime value for the clear-sky direct radiative forcing due to rBC from 23 December 2012 to 31 January 2013 was 47.7 &plusmn; 28.9 W m 2, which amounted to an average of 45.7% of the total surface atmospheric aerosol forcing.</p