Tianxue Wen

Aerosol optical depth (AOD) and Angstrom exponent of aerosols observed by the Chinese Sun Hazemeter Network from August 2004 to September 2005

500, and 650 nm were analyzed for the period of August 2004 to September 2005. The smallest mean AOD (0.15) was found in the Tibetan Plateau where a showed the largest range in value (0.06‐0.9). The remote northeast corner of China was the next cleanest region with AODs ranging from 0.19 to 0.21 and with the largest a (1.16‐1.79), indicating the presence of fine aerosol particles. The forested sites exhibited moderate values of AOD (0.19‐0.51) and a (0.97‐1.47). A surprising finding was that the AOD measured at a few desert sites in northern China were relatively low, ranging from 0.24 to 0.36, and that a ranged from 0.42 to 0.99, presumably because of several dustblowing episodes during the observation period. The AOD observed over agricultural areas ranges from 0.38 to 0.90; a ranges from 0.55 to 1.11. These values do not differ much from those observed at the inland urban and suburban sites where AOD ranges from 0.50 to 0.69 and a ranges from 0.90 to 1.48. Given the geographic heterogeneity and the rapid increase in urbanization in China, much longer and more extensive observations are required.

Size-resolved aerosol chemical analysis of extreme haze pollution events during early 2013 in urban Beijing, China

Using size-resolved filter sampling and chemical characterization, high concentrations of water-soluble ions, carbonaceous species and heavy metals were found in both fine (PM2.1) and coarse (PM2.1-9) particles in Beijing during haze events in early 2013. Even on clear days, average mass concentration of submicron particles (PM1.1) was several times higher than that previously measured in most of abroad urban areas. A high concentration of particulate matter on haze days weakens the incident solar radiation, which reduces the generation rate of secondary organic carbon in PM1.1. We show that the peak mass concentration of particles shifted from 0.43-0.65μm on clear days to 0.65-1.1μm on lightly polluted days and to 1.1-2.1μm on heavily polluted days. The peak shifts were also found for the following species: organic carbon, elemental carbon, NH4(+), SO4(2-), NO3(-), K, Cu, Zn, Cd and Pb. Our findings demonstrate that secondary inorganic aerosols (36%) and organic matter (26%) dominated the fine particle mass on heavily polluted days, while their contribution reduced to 29% and 18%, respectively, on clear days. Besides fine particles, anthropogenic chemical species also substantially accumulated in the coarse mode, which suggests that particles with aerodynamic diameter larger than 2.1μm cannot be neglected during severe haze events.

The Campaign on Atmospheric Aerosol Research Network of China: CARE-China

AbstractBased on a network of field stations belonging to the Chinese Academy of Sciences (CAS), the Campaign on Atmospheric Aerosol Research network of China (CARE-China) was recently established as the country’s first monitoring network for the study of the spatiotemporal distribution of aerosol physical characteristics, chemical components, and optical properties, as well as aerosol gaseous precursors. The network comprises 36 stations in total and adopts a unified approach in terms of the instrumentation, experimental standards, and data specifications. This ongoing project is intended to provide an integrated research platform to monitor online PM2.5 concentrations, nine-size aerosol concentrations and chemical component distributions, nine-size secondary organic aerosol (SOA) component distributions, gaseous precursor concentrations (including SO2, NOx, CO, O3, and VOCs), and aerosol optical properties. The data will be used to identify the sources of regional aerosols, the relative contributions fr...

In situ measurements of aerosol mass concentration and radiative properties in Xianghe, southeast of Beijing

measurements showed an average concentration of 120 mg/m 3 in the coarse mode and an average concentration of 25 mg/m 3 in the fine mode. To determine how representative ground-based measurements are of the total column, the mass concentration data was compared with AERONET AOT at 500 nm and AERONET size distribution data. The vertical distribution of the aerosols were studied with a micropulse lidar and in the cases where the vertical column was found to be fairly homogenous, the comparisons of the filter results with AERONET agreed favorably, while in the cases of inhomogeneity, the comparisons have larger disagreement. For fine mode aerosols, the average spectral absorption efficiency equates well to a l 1 model, while the coarse mode shows a much flatter spectral dependence, consistent with large particle models. The coarse mode absorption efficiency was compatible with that of the fine mode in the NIR region, indicating the much stronger absorption of the coarse mode due to its composition and sizable mass. Single scattering albedo results are presented from a combination between absorption coefficients derived from the filter measurements, from a PSAP and from a three-wavelength Nephelometer.

Spatial and seasonal variations of isoprene secondary organic aerosol in China: Significant impact of biomass burning during winter.

Isoprene is a substantial contributor to global secondary organic aerosol (SOA). The formation of isoprene SOA (SOAI) is highly influenced by anthropogenic emissions. Currently, there is rare information regarding SOAI in polluted regions. In this study, one-year concurrent observation of SOAI tracers was undertaken at 12 sites across China for the first time. The tracers formed from the HO2-channel exhibited higher concentrations at rural sites, while the tracer formed from the NO/NO2-channel showed higher levels at urban sites. 3-Methyltetrahydrofuran-3,4-diols exhibited linear correlations with their ring-opening products, C5-alkenetriols. And the slopes were steeper in the southern China than the northern China, indicating stronger ring-opening reactions there. The correlation analysis of SOAI tracers with the factor determining biogenic emission and the tracer of biomass burning (levoglucosan) implied that the high level of SOAI during summer was controlled by biogenic emission, while the unexpected increase of SOAI during winter was largely due to the elevated biomass burning emission. The estimated secondary organic carbon from isoprene (SOCI) exhibited the highest levels in Southwest China. The significant correlations of SOCI between paired sites implied the regional impact of SOAI in China. Our findings implicate that isoprene origins and SOAI formation are distinctive in polluted regions.

Quantification of the impact of aerosol on broadband solar radiation in North China

PM2.5 plays a key role in the solar radiation budget and air quality assessments, but observations and historical data are relatively rare for Beijing. Based on the synchronous monitoring of PM2.5 and broadband solar radiation (Rs), a logarithmic function was developed to describe the quantitative relationship between these parameters. This empirical parameterization was employed to calculate Rsn from PM2.5 with normalized mean bias (NMB) −0.09 and calculate PM2.5 concentration from Rsn with NMB −0.12. Our results indicate that this parameterization provides an efficient and straightforward method for estimating PM2.5 from Rs or Rs from PM2.5.

Characterization and source identification of fine particulate matter in urban Beijing during the 2015 Spring Festival

The Spring Festival (SF) is the most important holiday in China for family reunion and tourism. During the 2015 SF an intensive observation campaign of air quality was conducted to study the impact of the anthropogenic activities and the dynamic characteristics of the sources. During the study period, pollution episodes frequently occurred with 12days exceeding the Chinese Ambient Air Quality Standards for 24-h average PM2.5 (75μg/m3), even 8days with exceeding 150μg/m3. The daily maximum PM2.5 concentration reached 350μg/m3 while the hourly minimum visibility was <0.8km. Three pollution episodes were selected for detailed analysis including chemical characterization and diurnal variation of the PM2.5 and its chemical composition, and sources were identified using the Positive Matrix Factorization model. The first episode occurring before the SF was characterized by more formation of SO42- and NO3- and high crustal enrichment factors for Ag, As, Cd, Cu, Hg, Pb, Se and Zn and seven categories of pollution sources were identified, whereby vehicle emission contributed 38% to the PM2.5. The second episode occurring during the SF was affected heavily by large-scale firework emissions, which led to a significant increase in SO42-, Cl-, OC, K and Ba; these emissions were the largest contributor to the PM2.5 accounting for 36%. During the third episode occurring after the SF, SO42-, NO3-, NH4+ and OC were the major constituents of the PM2.5 and the secondary source was the dominant source with a contribution of 46%. The results provide a detailed understanding on the variation in occurrence, chemical composition and sources of the PM2.5 as well as of the gaseous pollutants affected by the change in anthropogenic activities in Beijing throughout the SF. They highlight the need for limiting the firework emissions during Chinas most important traditional festival.

Characteristics of complex air pollution in typical cities of North China

Abstract The Beijing–Tianjin–Hebei urban agglomeration is currently facing severe complex air pollution. In this paper, simultaneous observations conducted in 2014 show that the annual mean concentration of fine particulate matter (PM2.5) was 84 ± 70, 86 ± 60, and 118 ± 95 μg m−3 in Beijing, Tianjin, and Shijiazhuang, respectively. The mean O3_8 h max in the summer was 171 ± 43, 147 ± 45, and 146 ± 44 μg m−3, respectively. This research indicates that PM2.5 and O3 are positively correlated when the temperature exceeds 20 °C, and the urban agglomeration shows characteristics of complex air pollution consisting of superimposed O3 and PM2.5. In summer, when the humidity was less than 55%, secondary particles and O3 also increased in a coordinated manner (y = 1.35x + 29.85; R2 = 0.61), which demonstrates severe complex pollution. However, the mean PM2.5 (y) and mean O3_8 h max (x) in summer showed a negative correlation (y = −1.3x + 245; R2 = 0.61) in the three regions, indicating high concentrations of PM2.5 pollution partially inhibit O3 generation.

Effects of transport on aerosols over the eastern slope of the Tibetan Plateau: synergistic contribution of Southeast Asia and the Sichuan Basin

ABSTRACT The aerosol optical properties and chemical components of PM2.1 (particulate matter with a diameter of 2.1 µm or less) were investigated at Mount Gongga on the eastern slope of the Tibetan Plateau from April 2012 to December 2014. The annual mean aerosol optical depth (AOD) was 0.35 ± 0.23, and the Ångström exponent was 1.0 ± 0.38. The AOD exhibited higher values in summer and winter, but lower values in spring and autumn. Dividing the observational periods into dry and wet seasons, the authors found that the concentrations of K+, elemental carbon, secondary inorganic aerosols, and primary and secondary organic carbon in the dry (wet) season were 0.29 (0.21), 0.88 (0.60), 7.4 (4.5), 7.5 (5.1), and 3.9 (12) µg m−3, respectively. Combined with trajectory analysis, the authors found that higher concentrations of K+, elemental carbon, and primary organic carbon indicated the effects of biomass burning from Southeast Asia during the dry season. However, the oxidation of volatile organic compounds was the main source of aerosols during the wet season, which originated from the Sichuan Basin. Graphical Abstract