Spatial and seasonal variability of water-soluble ions in PM2.5 aerosols in 14 major cities in China

We analyzed PM2.5 aerosols from 14 major cities in China for concentrations of water-soluble (WS) major and trace elements (Na, Mg, Ca, K, Fe, Mn, Zn, Rb, Sr, Ba, Pb, S and Cl). The main focus was to examine patterns in spatial distribution and seasonal variability. Using principal component analysis, we identified three general sources for WS-elements in aerosols as anthropogenic, seasalts and fine dust particles originating from soils. The spatial patterns identified show that anthropogenic activity is the most important factor influencing the concentration of heavy metals in aerosols. Concentrations of WS-S, Zn and Pb were correlated with the locations of major industrial zones, and regulated by topography and seasonal weather patterns. We found higher WS-metals concentrations during the winter season, probably related to coal combustion in northern China. Moderate correlations of WS-S, Zn, Pb and Cl suggest that coal combustion releases. The seasonal pattern in WS-Fe concentrations shows the importance of acid precipitation events where coal combustion contributes to additional Fe (II) deposition. The findings of this study support the argument that WS-S in fine particles enhanced the production of hydrogen ions act to reduce the pH values of precipitation. Our interpretation of these spatial and seasonal patterns in WS-major and trace elements in aerosols highlights the need for continued research on trends in acidic deposition in major industrial cities in China.</p

Carbonaceous Aerosol Characteristics in Outdoor and Indoor Environments of Nanchang, China, during Summer 2009

A study of carbonaceous aerosol was initiated in Nanchang, a city in eastern China, for the first time. Daily and diurnal (daytime and nighttime) PM(2.5) (particulate matter with aerodynamic diameter &lt;= 2.5 mu m) samples were collected at an outdoor site and in three different indoor environments (common office, special printing and copying office, and student dormitory) in a campus of Nanchang University during summer 2009 (5-20 June). Daily PM(10) (particulate matter with aerodynamic diameter &lt;= 10 mu m) samples were collected only at the outdoor site, whereas PM(2.5) samples were collected at both indoor and outdoor sites. Loaded PM(2.5) and PK(10) samples were analyzed for organic and elemental carbon (OC, EC) by thermal/optical reflectance following the Interagency Monitoring of Protected Visual Environments-Advanced (IMPROVE-A) protocol. Ambient mass concentrations of PM(10) and PM(2.5) in Nanchang were compared with the air quality standards in China and the United States, and revealed high air pollution levels in Nanchang. PM(2.5) accounted for about 70% of PM(10), but the ratio of OC and EC in PM(2.5) to that in PK(10) was higher than 80%, which indicated that OC and EC were mainly distributed in the fine particles. The variations of carbonaceous aerosol between daytime and nighttime indicated that OC was released and formed more rapidly in daytime than in nighttime. OC/EC ratios were used to quantify secondary organic carbon (SOC). The differences in SOC and SOC/OC between daytime and nighttime were useful in interpreting the secondary formation mechanism. The results of (1) OC and EC contributions to PM(2.5) at indoor sites and the outdoor site; (2) indoor-outdoor correlation of OC and EC; (3) OC-EC correlation; and (4) relative contributions of indoor and outdoor sources to indoor carbonaceous aerosol indicated that OC indoor sources existed in indoor sites, with the highest OC emissions in 12 (the special printing and copying office), and that indoor EC originated from outdoor sources. The distributions of eight carbon fractions in emissions from the printer and copier showed obviously high OC1 (&gt; 20%) and OC2 (similar to 30%), and obviously low EC1-OP (a pyrolyzed carbon fraction) (&lt; 10%), when compared with other sources.</p

Numerical Simulation of the Micro Environment in the Han Yang Mausoleum Museum

As a first underground museum in the world, whole sealed glass system is adopted in the Han Yang Mausoleum Museum to protect relics from the destruction by microbe and pollution in the atmosphere and to provide visitors a wonderful environment for enjoying the fantastic artwork closely from different angles. This study shows that, this method cannot completely stop relics from the destruction. The main reason is that, in the museum, the microbe growth and pollution spread are fairly significant to affect the protection of relics. This study numerically simulates the micro environment in the museum, including air movement, temperature and relative humidity by using the CFD software Fluent. The major findings are summaried as the followes: there are four air cyclones; temperature is getting lower from one side to another; and relative humidity profile is reversed, especially at the surface. This numerical result provides useful information for the protection of relics.</p

Molecular distribution and seasonal variation of hydrocarbons in PM2.5 from Beijing during 2006

Normal (n)-alkanes and polycyclic aromatic hydrocarbons (PAHs) in PM2.5 were collected from Beijing in 2006 and analyzed using a thermal desorption-GC/MS technique. Annual average concentrations of n-alkanes and PAHs were 282 +/- 96 and 125 +/- 150 ng/m(3), respectively: both were highest in winter and lowest in summer. C-19-C-25 compounds dominated the n-alkanes while benzo[b]fluoranthene, benzo[e]pyrene, and phenanthrene were the most abundant PAHs. The n-alkanes exhibited moderate correlations with organic carbon (OC) and elemental carbon (EC) throughout the year, but the relationships between the PAHs, OC and EC differed between the heating and non-heating seasons. The health risks associated with PAHs in winter were more than 40 times those in spring and summer even though the PM2.5 loadings were comparable. Carbon preference index values (&lt;1.5) indicated that the n-alkanes were mostly from fossil fuel combustion. The ratios of indeno[123-cd]pyrene to benzo[ghi]pyrelene in summer and spring were 0.58 +/- 0.12 and 0.63 +/- 0.09, respectively, suggesting that the PAHs mainly originated from motor vehicles, but higher ratios in winter reflected an increased influence from coal, which is extensively burned for domestic heating. A comprehensive comparison showed that PAH pollution in Beijing has decreased in the past 10 years.</p

Evolution of PM2.5 Measurements and Standards in the US and Future Perspectives for China

National Ambient Air Quality Standards (NAAQS) were first established in the United States to protect public health and welfare, and the concept has been adopted in China and many other countries. For particulate matter (PM), the NAAQS indicator evolved from total particle mass concentration, to PM10 and PM2.5 mass concentrations as defined by the PM size-selective properties of the monitoring instrument and human inhalation characteristics. Particle measurements started with optical microscopy in the early 18th century, and scientific research over the past 300 years has related particles to adverse environmental and health effects. Several options for PM2.5 measurement and assessment are available to China and other developing countries as they implement new PM2.5 ambient air quality standards. Although much can be learned from the experience of North America and Europe, China can leapfrog ahead in terms of PM2.5 monitoring and emission reduction technology. China-specific guidance documents should be created for network design, equipment selection and operation, quality control and quality assurance, database management, and interpretation. Future air quality management and standards will need to consider multiple pollutants and their effects on visibility, climate, materials, and ecosystems in addition to the primary concerns about public health.</p

A budget analysis of the formation of haze in Beijing

During recent winters, hazes often occurred in Beijing, causing major environmental problems. To understand the causes of this &ldquo;Beijing Haze&rdquo;, a haze episode (from Oct. 21 to Oct. 31, 2013) in Beijing was analyzed. During the episode, the daily mean concentration of fine particulate matter (PM2.5) reached a peak value of 270&nbsp;&mu;g/m3 on Oct. 28, 2013, and rapidly decreased to 50&nbsp;&mu;g/m3 the next day (Oct. 29, 2013). This strong variability provided a good opportunity to study the causes of a &ldquo;Beijing Haze&rdquo;. Two numerical models were applied for this study. The first model is a chemical/dynamical regional model (WRF-Chem). This model is mainly used to study the effects that weather conditions have on PM2.5 concentrations in the Beijing region. The results show that the presence of high air pressure in northwest Beijing (NW-High) generally produced strong northwest winds with clean upwind air. As a result, the NW-High played an important role in cleaning Beijing&#39;s PM. However, the NW-High&#39;s cleaning effect did not occur in every situation. When there was low air pressure in southeast Beijing (SE-Low) accompanied by an NW-High, an air convergent zone appeared in Beijing. The pollutants became sandwiched, producing high PM2.5 concentrations in the Beijing region. The second model used in this study is a box model, which is applied to estimate some crucial parameters associated with the budget of PM2.5 in the Beijing region. Under calm winds, the calculations show that continuous local emissions rapidly accumulate pollutants. The PM2.5 concentrations reached 150&nbsp;&mu;g/m3 and 250&nbsp;&mu;g/m3 within one (1) day and two (2) days, respectively. Without horizontal dilution, this estimate can be considered as an upper time limit (the fastest time) for the occurrences of haze events in the Beijing region. The wind speed (WSb) is calculated for the balance between the continuous emissions and atmospheric clean processes. The results show that the WSb is strongly dependent on the planetary boundary layer (PBL) height and the wind direction. Under SE-Low weather conditions, the WSb is 2&nbsp;m/s with a higher PBL height (700&nbsp;m). However, under lower PBL heights, the WSb rapidly increases, reaching 4.5&nbsp;m/s and 7.0&nbsp;m/s with PBL heights of 300&nbsp;m and 200&nbsp;m, respectively. In contrast, under NW-High weather conditions, the WSb reduces to 2.5&nbsp;m/s and 4.0&nbsp;m/s. These results suggest that when the prevailing wind in Beijing is a northwest wind (with wind speeds of &gt;4&nbsp;m/s), particulate matter (PM) begins to decrease.</p

Multi-Year Analyses of Columnar Aerosol Opticaland Microphysical Properties in Xi’an, a Megacity inNorthwestern China

A thorough understanding of aerosol optical properties and their spatio-temporal variability are required to accurately evaluate aerosol effects in the climate system. In this study, a multi-year study of aerosol optical and microphysical properties was firstly performed in Xi’an based on three years of sun photometer remote sensing measurements from 2012 to 2015. The multi-year average of aerosol optical depth (AOD) at 440 nm was about 0.88 ± 0.24 (mean ± SD), while the averaged Ångström Exponent (AE) between 440 and 870 nm was 1.02 ± 0.15. The mean value of single scattering albedo (SSA) was around 0.89 ± 0.03. Aerosol optical depth and AE showed different seasonal variation patterns. Aerosol optical depth was slightly higher in winter (0.99 ± 0.36) than in other seasons (~0.85 ± 0.20), while AE showed its minimum in spring (0.85 ± 0.05) due to the impact of dust episodes. The seasonal variations of volume particle size distribution, spectral refractive index, SSA, and asymmetry factor were also analyzed to characterize aerosols over this region. Based on the aerosol products derived from sun photometer measurements, the classification of aerosol types was also conducted using two different methods in this region. Results show that the dominant aerosol types are absorbers in all seasons, especially in winter, demonstrating the strong absorptivity of aerosols in Xi’an

Column-Integrated Aerosol Optical Properties during Summer and Autumn of 2012 in Xi'an, China

Column-integrated aerosol optical properties were derived systematically from measurements made in Xi&#39;an, which is located in Guanzhong Plain of central China with a ground-based CIMEL sun photometer from May to November 2012. Aerosol optical depths (AODs), Angstrom exponents, water vapor contents, and aerosol optical and micro-physical properties, including aerosol volume size distribution, complex refractive indices and single scattering albedo (SSA), were determined. Daily variations in AODs at 440 nm (tau(440)) generally followed those of the 24-hr PM2.5 mass concentrations, but there were differences in the relationships in summer and autumn. August showed the highest monthly tau(440) (1.13) while the largest monthly Angstrom exponent (alpha(440-870) = 1.30) and water vapor content (C-w = 4.28) both occurred in July. Monthly averages of the aerosol size distributions showed the dominance of coarse mode aerosols, except in July and August, when the contribution of the accumulation and coarse modes were fairly comparable. Monthly changes in the complex refractive index (including both real and imaginary parts) and SSA were also studied, including their wavelength dependences; these analyses implied changes in the abundances of the aerosol types. Finally, an episode involving urban and dust aerosols was analyzed using sun photometer aerosol retrievals; MODIS images captured by Aqua satellite and average wind vectors from the NCEP operational global analyses were also considered in the case study.</p

Fine Particulate Matter Constituents and Cardiopulmonary Mortality in a Heavily Polluted Chinese City

BACKGROUND: Although ambient fine particulate matter (PM(2.5); particulate matter &lt;= 2.5 mu m in aerodynamic diameter) has been linked to adverse human health effects, the chemical constituents that cause harm are unknown. To our knowledge, the health effects of PM(2.5) constituents have not been reported for a developing country. OBJECTIVES: We examined the short-term association between PM(2.5) constituents and daily mortality in Xi&#39;an, a heavily polluted Chinese city. METHODS: We obtained daily mortality data and daily concentrations of PM(2.5), organic carbon (OC), elemental carbon (EC), and 10 water-soluble ions for 1 January 2004 through 31 December 2008. We also measured concentrations of fifteen elements 1 January 2006 through 31 December 2008. We analyzed the data using overdispersed generalized linear Poisson models. RESULTS: During the study period, the mean daily average concentration of PM(2.5) in Xi&#39;an was 182.2 mu g/m(3). Major contributors to PM(2.5) mass included OC, EC, sulfate, nitrate, and ammonium. After adjustment for PM(2.5) mass, we found significant positive associations of total, cardiovascular, or respiratory mortality with OC, EC, ammonium, nitrate, chlorine ion, chlorine, and nickel for at least one lag period. Nitrate demonstrated stronger associations with total and cardiovascular mortality than PM(2.5) mass. For a 1-day lag, interquartile range increases in PM(2.5) mass and nitrate (114.9 and 15.4 mu g/m(3), respectively) were associated with 1.8% [95% confidence interval (CI): 0.8%, 2.8%] and 3.8% (95% CI: 1.7%, 5.9%) increases in total mortality, CONCLUSIONS: Our findings suggest that PM(2.5) constituents from the combustion of fossil fuel may have an appreciable influence on the health effects attributable to PM(2.5) in Xi&#39;an.</p

Long-term trends in chemical composition of precipitation at Lijiang, southeast Tibetan Plateau, southwestern China

1090 precipitation samples were collected between 1989 and 2006 from the Lijiang region, an internationally important tourist site in Yunnan province, southwestern China. All the samples were analyzed for pH, electrical conductivity, SO4 2&minus;, Cl&minus;, NO3 &minus;, Na+, Ca2+, Mg2+ and NH4 + concentrations. pH had a mean value of 6.08 and showed a slight increase as tourism developed between 1989 and 2006. SO4 2&minus; and Ca2+ were the dominant anion and cation, respectively. Most of the ions showed significantly increasing trends, especially Ca2+ and Mg2+, with the exception of NH4 + that had a clearly decreasing trend. As a result, the neutralization capacity of Ca2+ increased significantly, and the precipitation NP/AP (neutralizing potential index/ acidifying potential index) ratio increased. There was a significant correlation between the soil-derived cations Ca2+ and Mg2+, and significant correlation of SO4 2&minus; with Ca2+ and Mg2+. The sea-salt species Cl&minus; and Na+ was not well correlated. Using Na+ as a sea-salt tracer, non-sea-salt source fractions were calculated as SO4 2&minus;: 99.1%, Mg2+: 92.6% and Ca2+: 99.8%. Furthermore, about 95.4% of NO3 &minus; and 41.7% of SO4 2&minus; were contributed by anthropogenic sources, and 57.4% of SO4 2&minus; was contributed by soil/dust sources that had a remarkably strong relationship (r=0.65, pb0.01) with the number of tourists, suggesting that human activities in a tourism-oriented city increase atmospheric dust loading.</p