Photochemical properties and source of pollutants during continuous pollution episodes in Beijing, October, 2011

Review of online source apportionment research based on observation for ambient particulate matter

Particulate matter source apportionment (SA) is the basis and premise for preventing and controlling haze pollution scientifically and effectively. Traditional offline SA methods lack the capability of handling the rapid changing pollution sources during heavy air pollution periods. With the development of multiple online observation techniques, online SA of particulate matter can now be realized with high temporal resolution, stable and reliable continuous observation data on particle compositions. Here, we start with a summary of online measuring instruments for monitoring particulate matters that contains both online mass concentration (online MC) measurement, and online mass spectrometric (online MS) techniques. The former technique collects ambient particulate matter onto filter membrane and measures the concentrations of chemical components in the particulate matter subsequently. The latter technique could be further divided into two categories: bulk measurement and single particle measurement. Aerosol Mass Spectrometers (AMS) could provide mass spectral information of chemical components of non-refractory aerosols, especially organic aerosols. While the emergence of single-particle aerosol mass spectrometer (SPAMS) technology can provide large number of high time resolution data for online source resolution. This is closely followed by an overview of the methods and results of SA. However, online instruments are still facing challenges, such as abnormal or missing measurements, that could impact the accuracy of online dataset. Machine leaning algorithm are suited for processing the large amount of online observation data, which could be further considered. In addition, the key research challenges and future directions are presented including the integration of online dataset from different online instruments, the ensemble-trained source apportionment approach, and the quantification of source-category-specific human health risk based on online instrumentation and SA methods.

Ambient air pollution and respiratory mortality in Xi'an, China: a time-series analysis

Background

Although air pollution is a known fundamental problem in China, few studies have investigated the associations between ambient air pollution and respiratory mortality in non-metropolitan cities of China. The study aimed to investigate a potential relationship between short-term exposure to ambient air pollutants and respiratory mortality in Xi’an, China.

Methods

Daily averages of PM_2.5, SO₂, O₃, temperature, relative humidity and daily counts of respiratory mortality were obtained (2014–2016). Using a single and multi-pollutant approach in time-series analysis, the generalized additive model with natural splines was used for analysis. Subgroup analysis stratified by gender and age group (≤ 64 years and ≥ 65 years) was conducted.

Results

Seven thousand nine hundred sixty-five cases of respiratory mortality were assessed, with 62.9, 28.5, and 8.6% of mortality attributed to chronic lower respiratory diseases, influenza and pneumonia, as well as other forms of respiratory diseases, respectively. Observed pollutants were significantly associated with respiratory mortality. In the single pollutant model, 10 μg/m³ increase in a two-day moving average of PM_2.5, and SO₂ concentrations were significantly associated with relative risk 1.313(1.032, 1.708) and 1.4020(0.827, 2.854) of respiratory mortality, respectively. The effects of both air pollutants remained statistically significant after adjusting for collinearity in the multi-pollutant model. Ozone was only statistically associated with respiratory mortality in females at lag 0 [RR: 0.964(0.938, 0.991)].

Conclusion

This study provided evidence that respiratory mortality in Xi’an was significantly associated with exposure to ambient air pollutants from 2014 to 2016.

Heterogeneous Uptake of N2O5 in Sand Dust and Urban Aerosols Observed during the Dry Season in Beijing

The uptake of dinitrogen pentoxide (N2O5) on aerosols affects the nocturnal removal of NOx and particulate nitrate formation in the atmosphere. This study investigates N2O5 uptake processes using field observations from an urban site in Beijing during April–May 2017, a period characterized by dry weather conditions. For the first time, a very large N2O5 uptake rate (k(N2O5) up to ~0.01 s−1) was observed during a sand storm event, and the uptake coefficient (γ(N2O5)) was estimated to be 0.044. The γ(N2O5) in urban air masses was also determined and exhibited moderate correlation (r = 0.68) with aerosol volume to surface ratio (Va/Sa), but little relation to aerosol water, nitrate, and chloride, a finding that contrasts with previous results. Several commonly used parameterizations of γ(N2O5) underestimated the field-derived γ(N2O5). A new parameterization is suggested for dry conditions, which considers the effect of Va/Sa, temperature, and relative humidity.

Characterization of criteria air pollutants in Beijing during 2014-2015

One year-long criteria air pollutants data collected in Beijing were analyzed in this paper, which can support the research on formation, transport and human health effects of air pollutants. This is the first time to study the spatial and temporal variations of criteria pollutants in Beijing using hourly observational data from 12 sites between June 2014 and May 2015 released by the Ministry of Environmental Protection (MEP) of China. Beijing is facing tremendous air pollution as the daily averaged PM_2.5 (particulate matter with aerodynamic diameter less than 2.5µm) concentrations in all sites exceeding the Chinese Ambient Air Quality Standards (CAAQS) Grade I & II standards (15 and 35µg/m³). Slightly differences in PM_2.5 and ozone (O₃) were observed between sites at the urban and rural areas. Pearson correlation coefficients show that most pollutants are temporally correlated in Beijing except for O₃. The coefficients of divergence (COD) indicate that PM_2.5 is associated at most sites with only one rural site (Dingling) having observable difference and one site may be insufficient for monitoring surrounding area. The 8h peak O₃ (O₃-8h) also correlates at different sites but with one urban site (Haidianquwanliu) different from others. In addition, an extreme PM_2.5 event (hourly average concentration exceeding 300μg/m³ for ~40h) was examined with the consideration of meteorological conditions. Southerly wind with low speed and high relative humidity allow the accumulation of pollutants while northerly wind with high speed and low relative humidity result in good air quality.

Mixing ratio and carbon isotopic composition investigation of atmospheric CO2 in Beijing, China

The stable isotope composition of atmospheric CO2 can be used as a tracer in the study of urban carbon cycles, which are affected by anthropogenic and biogenic CO2 components. Continuous measurements of the mixing ratio and δ(13)C of atmospheric CO2 were conducted in Beijing from Nov. 15, 2012 to Mar. 8, 2014 including two heating seasons and a vegetative season. Both δ(13)C and the isotopic composition of source CO2 (δ(13)CS) were depleted in the heating seasons and enriched in the vegetative season. The diurnal variations in the CO2 mixing ratio and δ(13)C contained two peaks in the heating season, which are due to the effects of morning rush hour traffic. Seasonal and diurnal patterns of the CO2 mixing ratio and δ(13)C were affected by anthropogenic emissions and biogenic activity. Assuming that the primary CO2 sources at night (22:00-04:00) were coal and natural gas combustion during heating seasons I and II, an isotopic mass balance analysis indicated that coal combustion had average contributions of 83.83±14.11% and 86.84±12.27% and that natural gas had average contributions of 16.17±14.11% and 13.16±12.27%, respectively. The δ(13)C of background CO2 in air was the main error source in the isotopic mass balance model. Both the mixing ratio and δ(13)C of atmospheric CO2 had significant linear relationships with the air quality index (AQI) and can be used to indicate local air pollution conditions. Energy structure optimization, for example, reducing coal consumption, will improve the local air conditions in Beijing.

Design and demonstration of a next-generation air quality attainment assessment system for PM2.5 and O3

Due to the increasingly stringent standards, it is important to assess whether the proposed emission reduction will result in ambient concentrations that meet the standards. The Software for Model Attainment Test-Community Edition (SMAT-CE) is developed for demonstrating attainment of air quality standards of O3 and PM2.5. SMAT-CE improves computational efficiency and provides a number of advanced visualization and analytical functionalities on an integrated GIS platform. SMAT-CE incorporates historical measurements of air quality parameters and simulated air pollutant concentrations under a number of emission inventory scenarios to project the level of compliance to air quality standards in a targeted future year. An application case study of the software based on the U.S. National Ambient Air Quality Standards (NAAQS) shows that SMAT-CE is capable of demonstrating the air quality attainment of annual PM2.5 and 8-hour O3 for a proposed emission control policy.

Chemical characteristics of water-soluble ions in particulate matter in three metropolitan areas in the North China Plain

PM_2.5 and PM₁₀ samples were collected simultaneously in each season in Beijing, Tianjin and Shijiazhuang to identify the characteristics of water-soluble ion compositions in the North China Plain. The water-soluble ions displayed significant seasonal variation. The dominant ions were NO₃⁻, SO₄²⁻, NH₄⁺ and Cl⁻, accounting for more than 90% and 86% to the mass of total water-soluble ions in PM_2.5 and PM₁₀, respectively. The anion/cation ratio indicated that the ion acidity of each city varied both between sites and seasonally. Over 50% of the ion species were enriched in small particles ≤1 µm in diameter. The [NO₃⁻]/[SO₄²⁻] ratio indicated that vehicles accounted for the majority of the particulate pollution in Beijing. Shijiazhuang, a city highly reliant on coal combustion, had a higher SO₄²⁻ concentration.