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

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

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

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

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

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

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

Development of source profiles and their application insource apportionment of PM2.5 in Xiamen, China

Ambient PM2.5 samples were collected at four sites in Xiamen, including Gulangyu (GLY), Hongwen (HW), Huli (HL) and Jimei (JM) during January, April, July and October 2013. Local source samples were obtained from coal burning power plants, industries, motor vehicles, biomass burning, fugitive dust, and sea salt for the source apportionment studies. The highest value of PM2.5 mass concentration and species related to human activities (SO4 2&ndash;, NO3 &ndash;, Pb, Ni, V, Cu, Cd, organic carbon (OC) and elemental carbon (EC)) were found in the ambient samples from HL, and the highest and lowest loadings of PM2.5 and its components occurred in winter and summer, respectively. The reconstructed mass balance indicated that ambient PM2.5 consisted of 24% OM (organic matter), 23% sulfate, 14% nitrate, 9% ammonium, 9% geological material, 6% sea salt, 5% EC and 10% others. For the source profiles, the dominant components were OC for coal burning, motor vehicle, biomass burning and sea salt; SO4 2&ndash; for industry; and crustal elements for fugitive dust. Source contributions were calculated using a chemical mass balance (CMB) model based on ambient PM2.5 concentrations and the source profiles. GLY was characterized by high contributions from secondary sulfate and cooking, while HL and JM were most strongly affected by motor vehicle emissions, and biomass burning and fugitive dust, respectively. The CMB results indicated that PM2.5 from Xiamen is composed of 27.4% secondary inorganic components, 20.8% motor vehicle emissions, 11.7% fugitive dust, 9.9% sea salt, 9.3% coal burning, 5.0% biomass burning, 3.1% industry and 6.8% others.</p

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

Impact of Meteorological Parameters and Gaseous Pollutants on PM2.5 and PM10Mass Concentrations during 2010 in Xi’an, China

Mass concentrations of PM2.5 and PM10 from the six urban/rural sampling sites of Xi&rsquo;an were obtained during two weeks of every month corresponding to January, April, July and October during 2010, together with the six meteorological parameters and the data of two precursors. The result showed that the average annual mass concentrations of PM2.5 and PM10 were 140.9 &plusmn; 108.9 &micro;g m&ndash;3 and 257.8 &plusmn; 194.7 &micro;g m&ndash;3, respectively. Basin terrain constrains the diffusion of PM2.5 and PM10 concentration spatially. High concentrations in wintertime and low concentrations in summertime are due to seasonal variations of meteorological parameters and cyclic changes of precursors (SO2 and NO2). Stepwise Multiple Linear Regression (MLR) analysis indicates that relative humidity is the main factor influencing on meteorological parameter. Entry MLR analysis suggests that SO2 from local coal-burning power plants is still the primary pollutant. Trajectory cluster results of PM2.5 at BRR indicate that the entrained urban pollutants carried by the westerly or winter monsoon forms the dominant regional pollution sources in winter and spring. Ultraviolet (UV) aerosol index verified the source and pathway of dust storm in spring.</p