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

Contributions of residential coal combustion to the air qualityin Beijing–Tianjin–Hebei (BTH), China: a case study

In the present study, the WRF-Chem model is used to assess contributions of residential coal combustion (RCC) emissions to the air quality in Beijing-Tianjin-Hebei (BTH) during a persistent air pollution episode from 9 to 25 January 2014. In general, the predicted temporal variations and spatial distributions of the mass concentrations of air pollutants are in good agreement with observations at monitoring sites in BTH. The WRF-Chem model also reasonably reproduces the temporal variations in aerosol species when compared with the aerosol mass spectrometer measurements in Beijing. The RCC emissions play an important role in the haze formation in BTH, contributing about 23.1% of PM2.5 (fine particulate matter) and 42.6% of SO2 during the simulation period on average. Organic aerosols dominate the PM2.5 from the RCC emissions in BTH, with a contribution of 42.8 %, followed by sulfate (17.1 %). The air quality in Beijing is remarkably improved when the RCC emissions in BTH and the surrounding areas are excluded in model simulations, with a 30% decrease in PM2.5 mass concentrations. However, if only the RCC emissions in Beijing are excluded, the local PM2.5 mass concentration is decreased by 18.0% on average. Our results suggest that the implementation of the residential coal replacement by clean energy sources in Beijing is beneficial to the local air quality. Should residential coal replacement be carried out in BTH and its surrounding areas, the air quality in Beijing would be improved remarkably. Further studies would need to consider uncertainties in the emission inventory and meteorological fields

Azaarenes in fine particulate matter from the atmosphereof a Chinese megacity

Azaarenes (AZAs) are toxicologically relevant organic compounds with physicochemical properties that are significantly different from the well-studied polycyclic aromatic hydrocarbons (PAHs). However, little is known about their concentrations, seasonal variations, fate, and relationship with PAHs in air. This paper reports the temporal variations in the concentrations and composition patterns of AZAs in PM2.5 that was sampled once per 6 days from outdoor air of Xi’an, China from July 2008 to August 2009. The concentrations of the ∑AZAs, quinoline (QUI), benzo[h]quinoline (BQI), and acridine (ACR) in PM2.5 were 213–6441, 185–520, 69–2483, and 10–3544 pg m−3, respectively. These concentrations were higher than those measured in urban areas of Western Europe. AZA compositional patterns were dominated by BQI and ACR. The high concentration of AZAs, high AZA/related PAH ratio, and the dominance of three-ring AZAs (BQI and ACR) in PM2.5 of Xi’an are all in contrast to observations from Western European and North American cities. This contrast likely reflects differences in coal type and the more intense use of coal in China. The PM2.5-bound concentration of AZA in winter season (W) was higher than during the summer season (S) with W/S ratios of 5.7, 1.4, 4.1, and 13, for ∑AZAs, QUI, BQI, and ACR, respectively. Despite their significantly different physicochemical properties, AZAs were significantly (p < 0.05) positively correlated with their related PAHs and pyrogenic elemental carbon. The changes in AZA concentrations were positively correlated with ambient pressure but negatively correlated with ambient temperature, wind speed, and relative humidity. This trend is similar to that observed for the related PAHs. We conclude that Xi’an and possibly other Chinese cities have higher emission of AZAs into their atmosphere because of the more pronounced use of coal. We also conclude that in spite of differences in physicochemical properties between AZAs and related PAHs, the atmospheric dynamics and relationships with meteorological factors of both compound groups are similar

Characterization, mixing state, and evolution of urban single particles inXi'an (China) during wintertime haze days

A Single Particle Aerosol Mass Spectrometer (SPAMS) was deployed in the urban area of Xi&#39;an to investigate size-resolved chemical composition and mixing state of single particles during the heavy haze episode occurred from January 13 to January 27 in 2013. Nine major single particle types were resolved with ART-2a algorithm including biomass burning (BB), Potassium-Secondary (KSec), elemental and organic Carbon (ECOC), sodium-potassium-rich ECOC (NaKECOC), sodium-potassium-rich-secondary (NaKSec), EC, OC, and Dust. Daily PM2.5 mass concentration was 213&nbsp;&plusmn;&nbsp;122&nbsp;&mu;g&nbsp;m&minus;&nbsp;3. ~&nbsp;96% of the ambient particles were carbonaceous and internally mixed with secondary species such as sulfate and nitrate. The major particle types were from combustion sources, including coal burning, biomass burning, and vehicle exhaust. Mixing state analysis suggests gas-to-particle conversion was an important mechanism forming organic species during the winter haze episode. The relative abundances of the aged particle types, such as KSec and NaKSec increased with the elevated RH when RH&nbsp;&lt;&nbsp;80%. The fraction of aged particles in terms of number concentration was prominent during high levels of PM2.5 under stagnant air conditions. This study gained new knowledge on atmospheric aerosol formation and evolution in urban environment heavy winter haze condition.</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

Indoor air quality at five site museums of Yangtze River civilization

The Yangtze River civilization, dating back to more than 7 thousand years ago, is one of the most historic culture aggregates in China. For long-term conservation of archaeological artifacts and historical ruins along the Yangtze River, indoor air quality at five site museums were investigated during summer and winter. Unstable microclimate conditions were observed at all five museums. The maximal seasonal variations in temperature and relative humidity were 25.7 C and 40.0%, respectively. The mass concentration of PM2.5 inside the museums remained at high levels, ranging from 33.9 to 79.6 mg/m3 in winter and from 52.8 to 113.0 mg/m3 in summer. Organic matter (OM) constituted a major fraction (39.3% e53.9% in summer, 22.1%e27.8% in winter) of total PM2.5. The results showed that besides short-term fluctuation and seasonal variation in microclimate conditions, infiltration of gaseous and particulate air pollutants should be of increasing concern at museums in Southern China.</p

Chemical composition of PM2.5 at a high–altitude regional backgroundsite over Northeast of Tibet Plateau

Aerosol samples were collected from a site near Qinghai Lake (QHL) on the northeastern margin of the Tibetan Plateau (TP) to investigate PM2.5 mass levels and chemical composition, especially their seasonal patterns and sources. The PM2.5 ranged from 5.7 to 149.7&nbsp;&mu;g m&ndash;3, and it was predominately crustal material (-40% on average). The combined mass of eight water&ndash;soluble inorganic ions ranged from 1.0 to 41.5&nbsp;&mu;g m&ndash;3, with the largest contributions from SO42&ndash; NO3-, and Ca2+. Low abundances of organic carbon (OC, range: 1.0 to 8.2&nbsp;&mu;g m&ndash;3) and elemental carbon (EC, 0.2 to 2.3&nbsp;&mu;g m&ndash;3) were found in QHL. Weak seasonality in the OC/EC ratio (4.5&plusmn;2.0) indicated simple and stable sources for carbonaceous particles. The water&ndash;soluble ions, OC and EC accounted for ~30%, 10% and 2% of the PM2.5, respectively. Water&ndash;soluble organic carbon (WSOC, range: 0.5 to 4.3&nbsp;&mu;g m&ndash;3) accounted for 47.8% of the OC. Both OC and WSOC were positively correlated with water&ndash;soluble K+(r=0.70 and 0.73 respectively), an indicator of biomass burning. Higher WSOC and stronger correlations between WSOC and EC in spring and winter compared with summer and autumn are evidence for primary biomass burning aerosols. The concentrations of mass and major compositions were 2&ndash;10 times higher than those for some TP or continental background sites but much lower than urban areas. Compared with particles produced from burning yak dung (a presumptive source material), PM2.5 had higher SO42&ndash;/OC ratios. The higher ratios were presumed as a result of fossil fuel combustion. After excluding data for dust storms events, the relative percentages of OM, EC, K+, NH4+, NO3&ndash; and mineral dust showed little difference among seasons despite different monsoons dominated in four seasons; implying that the PM2.5 sources were relatively stable. The results from QHL evidently reflect regional cha racteristics of the aerosol.</p

Indoor air quality at five site museums of Yangtze River civilization

The Yangtze River civilization, dating back to more than 7 thousand years ago, is one of the most historic culture aggregates in China. For long-term conservation of archaeological artifacts and historical ruins along the Yangtze River, indoor air quality at five site museums were investigated during summer and winter. Unstable microclimate conditions were observed at all five museums. The maximal seasonal variations in temperature and relative humidity were 25.7 C and 40.0%, respectively. The mass concentration of PM2.5 inside the museums remained at high levels, ranging from 33.9 to 79.6 mg/m3 in winter and from 52.8 to 113.0 mg/m3 in summer. Organic matter (OM) constituted a major fraction (39.3% e53.9% in summer, 22.1%e27.8% in winter) of total PM2.5. The results showed that besides short-term fluctuation and seasonal variation in microclimate conditions, infiltration of gaseous and particulate air pollutants should be of increasing concern at museums in Southern China.</p

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

A study of elevated pollution layer over the North China Plain using aircraft measurements

An elevated pollution layer (EPL) at altitude &sim;1700 m was observed over the North China Plain (NCP) in November 2016. The vertical profiles of aerosol loadings, chemical compositions and meteorological parameters were in-situ measured at both ground and aircraft platforms. The EPLs were observed simultaneously over Beijing and Baoding city (&sim;150 km distance between) with similar aerosol concentration and size distribution, indicating the impact of the EPL at regional scale. The synoptic and remote sensing analysis suggest the pollutants in the EPL may result from regional transport from the polluted southwest, and then elevated by the influence of anticyclone circulation and surrounding terrain. The descent air mass next day may lead to EPL entrainment and contribute to increased aerosol concentration at lower level. The non-refractory compositions measured by aerosol mass spectrometer showed more significant fraction of nitrate and secondary organics in the EPL compared to the other layers. The pollutants in the EPL was then mixed into the developed planetary boundary layer (PBL), leading to uniform distribution of aerosol composition. Such atmospheric stratification at high level and its subsequent impact on the lower level needs to be considered for the future radiative forcing study over this region.</p