Source-specific light absorption and radiative effects decreases and indications due to the lockdown.

The 'extreme' emission abatement during the lockdown (from the end of 2019 to the early 2020) provided an experimental period to investigate the corresponding source-specific effects of aerosol. In this study, the variations of source-specific light absorption (babs) and direct radiative effect (DRE) were obtained during and after the lockdown period by using the artificial neural network (ANN) and source apportionment environmental receptor model. The results showed that the babs decreased for all sources during the two periods. The most reductions were observed with ∼90% for traffic-related emissions (during the lockdown) and ∼85% for coal combustion (after the lockdown), respectively. Heightened babs (370 nm) values were obtained for coal and biomass burning during the lockdown, which was attributed to the enhanced atmospheric oxidization capacity. Nevertheless, the variations of babs (880 nm) after the lockdown was mainly due to the weakening of oxidation and reduced emissions of secondary precursors. The present study indicated that the large-scale emission reduction can promote both reductions of babs (370 nm) and DRE (34-68%) during the lockdown. The primary emissions decrease (e.g., Traffic emission) may enhance atmosphere oxidation, increase the ultraviolet wavelength light absorption and DRE efficiencies. The source-specific emission reduction may be contributed to various radiation effects, which is beneficial for the adopting of control strategies.

[Case Analysis of Heavy Air Pollution Process in Xi'an Using Multi-source Data].

Air pollution continues to be a serious problem in Xi'an. A heavy pollution process and formation mechanism were investigated in Xi'an in January 2019 using multi-source methods (such as material balance and sulfur/nitrogen oxidation rate (SOR/NOR)). The multi-source data included the concentrations of PM2.5, PM10, SO2, NO2, CO, and O3; the chemical components of PM2.5; the meteorological records of ground and vertical observations; the atmospheric reanalysis data. Three phases were obtained including the accumulation phase (P1), maintenance phase (P2), and dispersion phase (P3) during the pollution period. The pollution event was primarily attributed to the superposition of adverse weather conditions and feedback effects. During the periods of P1 and P2, the area of Xi'an was affected by blocking and zonal westerly airflow at 500 hPa (with flat westerly airflow) and uniform-distribution pressure at sea level with a limited pressure gradient and stable weather conditions, and the easterly wind was dominant at 925 hPa; not all of these factors were conducive to the pollutant diffusion. An interaction feedback mechanism between meteorological conditions and heavy pollution could be studied using the ground-based microwave radiometer. The correlations between PM2.5 and inversions of water vapor density, relative humidity, air temperature, and temperature inversion were significant with coefficients of 0.86, 0.62, 0.53, and 0.38, respectively. The feedback mechanism was primarily manifested as follows:with the pollutant accumulation, the radiative cooling effect could lead to or strengthen the occurrence and intensity of temperature inversion, decrease the mixed layer height, and cause moisture accumulation. High humidity could further maintain the pollution by accelerating the secondary formation and promoting the hygroscopic growth of aerosol particles. Therefore, the dominant chemical components to PM2.5were secondary inorganic ions (SO42-+NO3-+NH4+, SNA) and "other" components during the period of P2, with contributions of 43.2% and 23.1%, respectively. In addition, the peak values of PM2.5, SOR, NOR, and the light extinction coefficients all occurred on the same days (January 3 and 6), indicating that the effect of secondary formation was important for both heavy pollution events and visibility. The total contribution of NH4NO3, organic matter (OM), (NH4)2SO4, and EC to the light extinction coefficient was more than 85%. Limited variations in the proportion for components were observed in three phases. During the period of P3, the strong cold air in the mid-lower atmosphere was conducive to the dry and clean air sinking and the pressure gradient at sea level increasing. These were beneficial to the diffusion of air pollutants and water vapor.

Enhanced Production of Organosulfur Species during a Severe Winter Haze Episode in the Guanzhong Basin of Northwest China.

The molecular composition of organic aerosols in ambient PM2.5 was investigated in an urban area in the Guanzhong basin of northwest China during a severe regional haze episode in the winter of 2018/2019. Organic matter, accounting for 20-35% of PM2.5 mass concentration, was characterized using direct infusion and electrospray ionization coupled with high-resolution Orbitrap mass spectrometry. The number of organic molecular formula assignments was primarily dominated by organosulfur species (OrgS, including CHOS and CHONS) in negative ion mode. The number and peak signal intensity of OrgS distinctly increased during the severe haze episode. Organosulfates and nitrooxy-organosulfates constituted the majority number (72-94%) of OrgS over the entire period. Although the OrgS were mostly present in aliphatic molecular structures, an increase in the number of polycyclic aromatic OrgS on haze days revealed the enhanced contribution from anthropogenic sources. The number of OrgS strongly correlated with ambient relative humidity and the oxidation ratios of sulfur and nitrogen, suggesting the important roles of aqueous phase chemistry and atmospheric oxidation in the formation of OrgS. A thorough understanding of the significance of OrgS will be essential to assess and mitigate the adverse impacts of haze pollution.

Variations of the urban PM2.5 chemical components and corresponding light extinction for three heating seasons in the Guanzhong Plain, China.

In order to investigate the variations of PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 µm) chemical components responding to the pollution control strategy and their effect on light extinction (bext) in the Guanzhong Plain (GZP), the comparisons of urban atmospheric chemical components during the heating seasons were extensively conducted for three years. The average concentration of PM2.5 decreased significantly from 117.9 ± 57.3 µg m-3 in the heating season 1 (HS1) to 53.5 ± 31.3 µg m-3 in the heating season 3 (HS3), which implied that the effective strategies were implemented in recent years. The greatest contribution to PM2.5 (∼30%) was from Organic matter (OM). The heightened contributions of the secondary inorganic ions (SNA, including NO3-, SO42-, and NH4+) to PM2.5 were observed with the values of 34% (HS1), 41% (HS2), and 42% (HS3), respectively. The increased percentages of NO3- contributions indicated that the emission of NOx should be received special attention in the GZP. The comparison of PM2.5 chemical compositions and implications across major regions of China and the globe were investigated. NH4NO3 was the most important contributor to bext in three heating seasons. The average bext was decreased from 694.3 ± 399.1 Mm-1 (HS1) to 359.3 ± 202.3 Mm-1 (HS3). PM2.5 had a threshold concentration of 75 µg m-3, 64 µg m-3, and 57 µg m-3 corresponding to the visual range (VR) < 10 km in HS1, HS2, and HS3, respectively. The enhanced impacts of the oxidant on PM2.5 and O3 were observed based on the long-term variations in PM2.5 and OX (Oxidant, the sum of O3 and NO2 mixing ratios) over the five heating seasons and PM2.5 and O3 over six summers from 2016 to 2021. The importance of coordinated control of PM2.5 and O3 was also investigated in the GZP.

Comparison of black carbon, primary and secondary brown carbon light absorption and direct solar absorption at the foothill and summit of Mt. Hua, China.

Atmospheric black carbon (BC), primary and secondary brown carbon (BrCpri and BrCsec) are the light-absorbing carbonaceous aerosol components. The vertical changes in the BC and BrC distributions are not generally known. Here, we presented a study of the spectral light absorption properties, direct solar absorption, and potential source areas of BC and BrC at the foothill (375 m a.s.l.) and summit (2060 m a.s.l.) of Mt. Hua, China. More than tripled BC and BrC light absorption coefficient were observed at the foothill compared to the summit. The dominant carbonaceous light-absorbing was attributed to BC with the percentages of 77 % (foothill) and 79 % (summit), respectively. The light absorption coefficient and direct solar absorption of BrCpri were much higher than those of BrCsec at foothill, especially in winter. The enhancing contributions of BrCsec light absorption coefficient and direct solar absorption were observed with high RH and visibility at the summit. The light absorption properties of BC, BrCpri, and BrCsec may be attributed to the emissions, meteorological conditions, and photochemical oxidation. The inferred potential source spatial distributions of BC and BrCpri showed different patterns at the foothill and summit. The results underlined the primary emission effects (including BC and BrCpri) at the foothill and the importance of BrCsec at the summit, respectively.

Concentration, optical characteristics, and emission factors of brown carbon emitted by on-road vehicles.

Atmospheric brown carbon (BrC) is a light-absorbing component that affects radiative forcing; however, this effect requires further clarification, particularly with respect to BrC emission sources, chromophores, and optical properties. In the present study, the concentrations, optical properties, and emission factors of organic carbon (OC), water-soluble OC (WSOC), and humic-like substances (HULIS) in fine particulate matter (PM2.5) emitted from vehicles in three road tunnels (the Wucun, Xianyue, and Wenxing tunnels in Xiamen, China) were investigated. The mass concentrations and light absorption of OC, WSOC, and HULIS were higher at the exits of each tunnel than at entrances, demonstrating that vehicle emissions were a BrC source. At each tunnel's exit, the average light absorption contributed by HULIS-BrC to water-soluble BrC (WS-BrC) and total BrC at 365 nm was higher than the corresponding carbon mass concentration contributed by HULIS (HULIS-C) to WSOC and OC, indicating that the chromophores of HULIS emitted from vehicles had a disproportionately high effect on the light absorption characteristics of BrC. The emission factors (EFs) of HULIS-C and WSOC mass concentrations were highest at the Xianyue tunnel; however, the EFs of HULIS-BrC and WS-BrC light absorption were highest at the Wenxing tunnel, indicating that the chromophore composition of BrC was different among the tunnels and that the mass concentration EFs did not correspond directly to the light absorption EFs.

Water-Insoluble Organics Dominate Brown Carbon in Wintertime Urban Aerosol of China: Chemical Characteristics and Optical Properties.

The chromophores responsible for light absorption in atmospheric brown carbon (BrC) are not well characterized, which hinders our understanding of BrC chemistry, the links with optical properties, and accurate model representations of BrC to global climate and atmospheric oxidative capacity. In this study, the light absorption properties and chromophore composition of three BrC fractions of different polarities were characterized for urban aerosol collected in Xi'an and Beijing in winter 2013-2014. These three BrC fractions show large differences in light absorption and chromophore composition, but the chromophores responsible for light absorption are similar in Xi'an and Beijing. Water-insoluble BrC (WI-BrC) fraction dominates the total BrC absorption at 365 nm in both Xi'an (51 ± 5%) and Beijing (62 ± 13%), followed by a humic-like fraction (HULIS-BrC) and high-polarity water-soluble BrC. The major chromophores identified in HULIS-BrC are nitrophenols and carbonyl oxygenated polycyclic aromatic hydrocarbons (OPAHs) with 2-3 aromatic rings (in total 18 species), accounting for 10% and 14% of the light absorption of HULIS-BrC at 365 nm in Xi'an and Beijing, respectively. In comparison, the major chromophores identified in WI-BrC are PAHs and OPAHs with 4-6 aromatic rings (in total 16 species), contributing 6% and 8% of the light absorption of WI-BrC at 365 nm in Xi'an and Beijing, respectively.

Wintertime Optical Properties of Primary and Secondary Brown Carbon at a Regional Site in the North China Plain.

The light-absorbing properties of atmospheric brown carbon (BrC) are poorly understood due to its complex chemical composition. Here, a black-carbon-tracer method was coupled with source apportionments of organic aerosol (OA) to explore the light-absorbing properties of primary and secondary BrC from the North China Plain (NCP). Primary emissions of BrC contributed more to OA light absorption than secondary processes, and biomass burning OA accounted for 60% of primary BrC absorption at λ = 370 nm, followed by coal combustion OA (35%) and hydrocarbon-like OA (5%). Secondary BrC absorption was high in the early morning and later decreased due to the bleaching of chromophores. Nighttime aqueous-phase chemistry promoted the formation of secondary light-absorbing compounds and the production of strongly absorbing particles. Source analysis showed that the NCP region was the most important source for primary and secondary BrC subtypes at the study site. The mean direct radiative forcing for BrC was 0.15 W m-2 (0.11 W m-2 and 0.04 W m-2 for the primary and secondary fractions, respectively). This study provides new information on the optical properties of primary and secondary BrC and highlights the importance of atmospheric oxidation on BrC absorption.

Exploring the impact of chemical composition on aerosol light extinction during winter in a heavily polluted urban area of China.

An intensive measurement campaign was conducted in Xi'an, China from December 2012-January 2013 to investigate the chemical composition, formation, and optical properties of PM1. The PM1 mass concentration (average = 138.8 ±â€¯83.2 µg m-3) accounted for ∼50% of the PM2.5 mass. Organic aerosols (OA) and secondary inorganic aerosols (SIA) were the most abundant PM1 components, contributing 53.0% and 35.0% to the mass, respectively. Both primary emissions and aqueous-phase oxidation of secondary aerosols played roles in the pollution episodes. The average light scattering and absorption coefficients during the campaign were 805 ±â€¯581 Mm-1 and 123 ±â€¯96 Mm-1, respectively. Both the mass scattering and mass absorption efficiencies for PM1 were higher than that for PM2.5-1, indicating stronger ability of light extinction for the smaller particles at visible wavelengths compared with the larger ones. The contributions of aerosol species to light extinction coefficients under two visibility conditions were estimated based on multiple linear regression models, and the OA was found to be the largest contributor to light extinction in both cases. A larger contribution of SIA to light extinction for visibility <5 km demonstrated its greater impacts on visibility during heavy pollution conditions. These findings provide insights into the importance of submicron particles for pollution and visibility degradation in northwestern China.

Contributions of local pollution emissions to particle bioreactivity in downwind cities in China during Asian dust periods.

This study investigated the effects of pollution emissions on the bioreactivity of PM2.5 during Asian dust periods. PM2.5 during the sampling period were 104.2 and 85.7 µg m-3 in Xi'an and Beijing, respectively, whereas PM2.5 which originated from the Tengger Desert was collected (dust background). Pollution conditions were classified as non-dust days, pollution episode (PE), dust storm (DS)-1, and DS-2 periods. We observed a significant decrease in cell viability and an increase in LDH that occurred in A549 cells after exposure to PM2.5 during a PE and DS-1 in Xi'an and Beijing compared to Tengger Desert PM2.5. Positive matrix factorization was used to identify pollution emission sources. PM2.5 from biomass and industrial sources contributed to alterations in cell viability and LDH in Xi'an, whereas vehicle emissions contributed to LDH in Beijing. OC, EC, Cl-, K+, Mg2+, Ca, Ti, Mn, Fe, Zn, and Pb were correlated with cell viability and LDH for industrial emissions in Xi'an during DS. OC, EC, SO42-, S, Ti, Mn, and Fe were correlated with LDH for vehicle emissions in Beijing during DS. In conclusion, the dust may carry pollutants on its surface to downwind areas, leading to increased risks of particle toxicity.

Chemical characterization of PM2.5 from a southern coastal city of China: applications of modeling and chemical tracers in demonstration of regional transport.

An intensive sampling campaign of airborne fine particles (PM2.5) was conducted at Sanya, a coastal city in Southern China, from January to February 2012. Chemical analyses and mass reconstruction were used identify potential pollution sources and investigate atmospheric reaction mechanisms. A thermodynamic model indicated that low ammonia and high relative humidity caused the aerosols be acidic and that drove heterogeneous reactions which led to the formation of secondary inorganic aerosol. Relationships among neutralization ratios, free acidity, and air-mass trajectories suggest that the atmosphere at Sanya was impacted by both local and regional emissions. Three major transport pathways were identified, and flow from the northeast (from South China) typically brought the most polluted air to Sanya. A case study confirmed strong impact from South China (e.g., Pearl River Delta region) (contributed 76.8% to EC, and then this result can be extended to primary pollutants) when the northeast winds were dominant. The Weather Research Forecasting Black carbon model and trace organic markers were used to apportion local pollution versus regional contributions. Results of the study offer new insights into the atmospheric conditions and air pollution at this coastal city.

Brown Carbon Aerosol in Urban Xi'an, Northwest China: The Composition 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 ( r2 > 0.61). These measured parent-PAHs and carbonyl-OPAHs account for on average ∼1.7% of the overall absorption of methanol-soluble BrC, about 5 times higher than their mass fraction in total organic carbon (OC, ∼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.

Morphologies and elemental compositions of local biomass burning particles at urban and glacier sites in southeastern Tibetan Plateau: Results from an expedition in 2010.

Many studies indicate that the atmospheric environment over the southern part of the Tibetan Plateau is influenced by aged biomass burning particles that are transported over long distances from South Asia. However, our knowledge of the particles emitted locally (within the plateau region) is poor. We collected aerosol particles at four urban sites and one remote glacier site during a scientific expedition to the southeastern Tibetan Plateau in spring 2010. Weather and backward trajectory analyses indicated that the particles we collected were more likely dominated by particles emitted within the plateau. The particles were examined using an electron microscope and identified according to their sizes, shapes and elemental compositions. At three urban sites where the anthropogenic particles were produced mainly by the burning of firewood, soot aggregates were in the majority and made up >40% of the particles by number. At Lhasa, the largest city on the Tibetan Plateau, tar balls and mineral particles were also frequently observed because of the use of coal and natural gas, in addition to biofuel. In contrast, at the glacier site, large numbers of chain-like soot aggregates (~25% by number) were noted. The morphologies of these aggregates were similar to those of freshly emitted ones at the urban sites; moreover, physically or chemically processed ageing was rarely confirmed. These limited observations suggest that the biomass burning particles age slowly in the cold, dry plateau air. Anthropogenic particles emitted locally within the elevated plateau region may thus affect the environment within glaciated areas in Tibet differently than anthropogenic particles transported from South Asia.

Light absorption properties of brown carbon over the southeastern Tibetan Plateau.

We present a study of the light-absorbing properties of water-soluble brown carbon (WS-BrC) and methanol-soluble brown carbon (MeS-BrC) at a remote site (Lulang, 3326m above sea level) in the southeastern Tibetan Plateau during the period 2015-2016. The light absorption coefficients at 365nm (babs365) of WS-BrC and MeS-BrC were the highest during winter and the lowest during monsoon season. MeS-BrC absorbs about 1.5 times higher at 365nm compared to WS-BrC. The absorption at 550nm appears lower compared to that of 365nm for WS-BrC and MeS-BrC, respectively. Higher average value of the absorption Ångström exponent (AAE, 365-550nm) was obtained for MeS-BrC (8.2) than that for WS-BrC (6.9). The values of the mass absorption cross section at 365nm (MAC365) indicated that BrC in winter absorbs UV-visible light more efficiently than in monsoon. The results confirm the importance of BrC in contributing to light-absorbing aerosols in this region. The understanding of the light absorption properties of BrC is of great importance, especially in modeling studies for the climate effects and transport of BrC in the Tibetan Plateau.

Spectral dependence of aerosol light absorption at an urban and a remote site over the Tibetan Plateau.

We present a study of aerosol light absorption by using a 7-wavelength Aethalometer model AE33 at an urban site (Lhasa) and a remote site (Lulang) in the Tibetan Plateau. Approximately 5 times greater aerosol absorption values were observed at Lhasa (53±46Mm-1 at 370nm and 20±18Mm-1 at 950nm, respectively) in comparison to Lulang (15±19Mm-1 at 370nm and 4±5Mm-1 at 950nm, respectively). Black carbon (BC) was the dominant light absorbing aerosol component at all wavelengths. The brown carbon (BrC) absorption at 370nm is 32±15% of the total aerosol absorption at Lulang, whereas it is 8±6% at Lhasa. Higher value of absorption Ångström exponent (AAE, 370-950nm) was obtained for Lulang (1.18) than that for Lhasa (1.04) due to the presence of BrC. The AAEs (370-950nm) of BrC were directly extracted at Lulang (3.8) and Lhasa (3.3). The loading compensation parameters (k) increased with wavelengths for both sites, and lower values were obtained at Lulang than those observed at Lhasa for all wavelengths. This study underlines the relatively high percentage of BrC absorption contribution in remote area compared to urban site over the Tibetan Plateau.

Concentration and sources of atmospheric nitrous acid (HONO) at an urban site in Western China.

Highly time-resolved measurements of nitrous acid (HONO) were carried out with a highly sensitive long path absorption photometer (LOPAP) at an urban site of Xi'an in Western China from 24 July to 6 August 2015 to investigate the atmospheric variations, sources, and formation pathways of HONO. The concentrations of HONO vary from 0.02 to 4.3ppbv with an average of 1.12ppbv for the entire measurement period. The variation trends of HONO and NO2 are very similar and positively correlated which, together with the similar diurnal profiles of HONO/NO2 ratio and HONO, suggest the importance of heterogeneous conversion of HONO from NO2. The nocturnal HONO level is governed by heterogeneous formation from NO2, followed by homogeneous formation of NO with OH and then by direct emissions. Further, it is found that the heterogeneous formation of HONO is largely affected by relative humidity and aerosol surface. Daytime HONO budget analysis indicates that an additional unknown source with HONO production rate of 0.75ppbvh-1 is required to explain the observed HONO concentration, which contributes 60.8% of the observed daytime HONO.

A 10-year observation of PM2.5-bound nickel in Xi'an, China: Effects of source control on its trend and associated health risks.

This study presents the first long term (10-year period, 2004-2013) datasets of PM2.5-bound nickel (Ni) concentration obtained from the daily sample in urban of Xi'an, Northwestern China. The Ni concentration trend, pollution sources, and the potential health risks associated to Ni were investigated. The Ni concentrations increased from 2004 to 2008, but then decreased due to coal consumption reduction, energy structure reconstruction, tighter emission rules and the improvement of the industrial and motor vehicle waste control techniques. With the comparison of distributions between workday and non-workday periods, the effectiveness of local and regional air pollution control policies and contributions of hypothetical Ni sources (industrial and automobile exhausts) were evaluated, demonstrating the health benefits to the populations during the ten years. Mean Ni cancer risk was higher than the threshold value of 10-6, suggesting that carcinogenic Ni still was a concern to the residents. Our findings conclude that there are still needs to establish more strict strategies and guidelines for atmospheric Ni in our living area, assisting to balance the relationship between economic growth and environmental conservation in China.

Two distinct patterns of seasonal variation of airborne black carbon over Tibetan Plateau.

Airborne black carbon (BC) mass concentrations were measured from November 2012 to June 2013 at Ranwu and Beiluhe, located in the southeastern and central Tibetan Plateau, respectively. Monthly mean BC concentrations show a winter (November-February) high (413.2ngm-3) and spring (March-June) low (139.1ngm-3) at Ranwu, but in contrast a winter low and spring high at Beiluhe (204.8 and 621.6ngm-3, respectively). By examining the meteorological conditions at various scales, we found that the monthly variation of airborne BC over the southeastern Tibetan Plateau (TP) was highly influenced by regional precipitation and over the hinterland by winds. Local precipitation at both sites showed little impact on the seasonal variation of airborne BC concentrations. Potential BC source regions are identified using air mass backward trajectory analysis. At Ranwu, BC was dominated by the air masses from the northeastern India and Bangladesh in both winter and spring, whereas at Beiluhe it was largely contributed by air masses from the south slope of Himalayas in winter, and from the arid region in the north of the TP in spring. The winter and spring seasonal peak of BC in the southern TP is largely contributed by emissions from South Asia, and this seasonal variation is heavily influenced by the regional monsoon. In the northern TP, BC had high concentrations during spring and summer seasons, which is very likely associated with more efficient transport of BC over the arid regions on the north of Tibetan Plateau and in Central Asia. Airborne BC concentrations at the Ranwu sampling site showed a significant diurnal cycle with a peak shortly after sunrise followed by a decrease before noon in both winter and spring, likely shaped by local human activities and the diurnal variation of wind speed. At the Beiluhe sampling site, the diurnal variation of BC is different and less distinct.

Chemical profiles of urban fugitive dust PM2.5 samples in Northern Chinese cities.

Urban fugitive dust PM2.5 samples were collected in 11 selected cities in North China, and 9 ions (SO4(2-), NO3(-), Cl(-), F(-), Na(+), NH4(+), K(+), Mg(2+), and Ca(2+)) and 22 elements (Si, Al, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Sr, Sn, Sb, Ba, and Pb) were determined to investigate chemical profiles of PM2.5. The coefficient of divergence (CD) was used to compare the similarities of the chemical profiles for fugitive dust among three regions in North China, and the results showed that their composition are quite similar. Total water soluble ions occupied 9.3% and 10.0% on average of road dust and construction dust, respectively, indicating that most of the materials in urban fugitive dust samples were insoluble. Ca(2+) was the most abundant cation and SO4(2-) dominated in anions. Soil dust loading was calculated to occupy 70.8% and 83.6% in road dust and construction dust, respectively. Ca, Si, Fe, and Al were the most abundant elements in all the samples, and Ca was absolutely the most abundant specie among the 22 detected elements in construction dust samples. Chemical species ratios were used to highlight the characteristics of urban fugitive dust by comparing with other types of aerosols. High Ca/Al ratio was a good marker to distinguish urban fugitive dust from Asian dust and Chinese loess. In addition, low K(+)/K and NO3(-)/SO4(2-), and high Zn/Al and Pb/Al ratios were good indicators to separate urban fugitive dust from desert dust, Chinese loess, or urban PM2.5 samples.

The rural carbonaceous aerosols in coarse, fine, and ultrafine particles during haze pollution in northwestern China.

The carbonaceous aerosol concentrations in coarse particle (PM10: Dp ≤ 10 µm, particulate matter with an aerodynamic diameter less than 10 µm), fine particle (PM2.5: Dp ≤ 2.5 µm), and ultrafine particle (PM0.133: Dp ≤ 0.133 µm) carbon fractions in a rural area were investigated during haze events in northwestern China. The results indicated that PM2.5 contributed a large fraction in PM10. OC (organic carbon) accounted for 33, 41, and 62 % of PM10, PM2.5, and PM0.133, and those were 2, 2.4, and 0.4 % for EC (elemental carbon) in a rural area, respectively. OC3 was more abundant than other organic carbon fractions in three PMs, and char dominated EC in PM10 and PM2.5 while soot dominated EC in PM0.133. The present study inferred that K(+), OP, and OC3 are good biomass burning tracers for rural PM10 and PM2.5, but not for PM0.133 during haze pollution. Our results suggest that biomass burning is likely to be an important contributor to rural PMs in northwestern China. It is necessary to establish biomass burning control policies for the mitigation of severe haze pollution in a rural area.