Significant Reduction in Fine Particulate Matter in Beijing during 2022 Beijing Winter Olympics

To investigate the air quality improvement during 2022 Beijing Winter Olympic Games (WOG), continuous hourly observations of fine particulate matter (PM2.5) and chemical fractions were performed in Beijing from January to March 2017–2022. Benefiting from the aggressive mitigation measures, significant reductions in the PM2.5 concentrations and chemical species in Beijing were observed during WOG. During strict control period, six sources of PM2.5 in Beijing were identified with positive matrix factorization model including secondary source (SS), industrial emissions (IEs), vehicle emissions (VEs), coal combustion (CC), fireworks burning (FB), and dust. Additionally, an obvious decline was observed in the sources of PM2.5, and no contribution of FB was quantitatively identified in 2022. Based on the multiple linear regression analysis, it found that meteorological parameters accounted for 46.1% of the total variation in the PM2.5 concentration, while source control measures accounted for 53.9% of the total variation, indicating that aggressive mitigation measures played a more important role in the decline in the PM2.5 concentration than meteorological conditions. This study could provide valuable insight into achieving air quality improvement and formulating policies in developing countries plagued by heavy air pollution

PAH contamination in road dust from a moderate city in North China: The significant role of traffic emission

<p>To investigate the contamination level, distribution, possible source, and human exposure risk of polycyclic aromatic hydrocarbons (PAHs) in the urban traffic environment, 15 PAHs were measured in 34 road dust samples (particle size < 25 μm) collected from three grades of roads and park paths in Xinxiang, China. ΣPAHs concentrations ranged from 311 to 21200 ng g⁻¹, with a mean of 5890 ng g⁻¹ and decreased in the following order: main roads (7650 ng g⁻¹) > collector streets (7410 ng g⁻¹) > bypasses (2970 ng g⁻¹) > park paths (1570 ng g⁻¹), indicating that significant positive correlation existed between PAH contamination and traffic density. PAHs in all samples were dominantly composed of 4-ring PAHs, accounting for 44.8% of the total. Pyrene, fluoranthene, and chrysene were the predominant individual components and accounted for 14.7% (1.2–19.2%), 12.9% (3.3–20.3%), and 11.0% (2.5–18.6%) of ΣPAHs, respectively. The specific isomer ratios indicated that traffic emission was the dominant source of PAHs in road dust. The incremental lifetime cancer risk values showed that cancer risk from exposure to road dust–borne PAHs was acceptable for local residents in Xinxiang.</p

Estimates of Health Impacts and Radiative Forcing in Winter Haze in Eastern China through Constraints of Surface PM_2.5 Predictions

The Gridpoint Statistical Interpolation (GSI) Three-Dimensional Variational (3DVAR) data assimilation system is extended to treat the MOSAIC aerosol model in WRF-Chem, and to be capable of assimilating surface PM_2.5 concentrations. The coupled GSI-WRF-Chem system is applied to reproduce aerosol levels over China during an extremely polluted winter month, January 2013. After assimilating surface PM_2.5 concentrations, the correlation coefficients between observations and model results averaged over the assimilated sites are improved from 0.67 to 0.94. At nonassimilated sites, improvements (higher correlation coefficients and lower mean bias errors (MBE) and root-mean-square errors (RMSE)) are also found in PM_2.5, PM₁₀, and AOD predictions. Using the constrained aerosol fields, we estimate that the PM_2.5 concentrations in January 2013 might have caused 7550 premature deaths in Jing-Jin-Ji areas, which are 2% higher than the estimates using unconstrained aerosol fields. We also estimate that the daytime monthly mean anthropogenic aerosol radiative forcing (ARF) to be −29.9W/m² at the surface, 27.0W/m² inside the atmosphere, and −2.9W/m² at the top of the atmosphere. Our estimates update the previously reported overestimations along Yangtze River region and underestimations in North China. This GSI-WRF-Chem system would also be potentially useful for air quality forecasting in China

Fossil Fuel Combustion-Related Emissions Dominate Atmospheric Ammonia Sources during Severe Haze Episodes: Evidence from ¹⁵N‑Stable Isotope in Size-Resolved Aerosol Ammonium

The reduction of ammonia (NH₃) emissions is urgently needed due to its role in aerosol nucleation and growth causing haze formation during its conversion into ammonium (NH₄⁺). However, the relative contributions of individual NH₃ sources are unclear, and debate remains over whether agricultural emissions dominate atmospheric NH₃ in urban areas. Based on the chemical and isotopic measurements of size-resolved aerosols in urban Beijing, China, we find that the natural abundance of ¹⁵N (expressed using δ¹⁵N values) of NH₄⁺ in fine particles varies with the development of haze episodes, ranging from −37.1‰ to −21.7‰ during clean/dusty days (relative humidity: ∼ 40%), to −13.1‰ to +5.8‰ during hazy days (relative humidity: 70–90%). After accounting for the isotope exchange between NH₃ gas and aerosol NH₄⁺, the δ¹⁵N value of the initial NH₃ during hazy days is found to be −14.5‰ to −1.6‰, which indicates fossil fuel-based emissions. These emissions contribute 90% of the total NH₃ during hazy days in urban Beijing. This work demonstrates the analysis of δ¹⁵N values of aerosol NH₄⁺ to be a promising new tool for partitioning atmospheric NH₃ sources, providing policy makers with insights into NH₃ emissions and secondary aerosols for regulation in urban environments

Evaluating urban and nonurban PM_2.5 variability under clean air actions in China during 2010–2022 based on a new high-quality dataset

The air quality in China has changed due to the implementation of clean air actions since 2013. Evaluating the spatial pattern of PM2.5 and the effectiveness of reducing anthropogenic emissions in urban and nonurban areas is crucial. Therefore, the China Long-term Air Pollutant dataset for PM2.5 (CLAP_PM2.5) was generated from 2010 to 2022 with a daily 0.1° resolution using the random forest model and integrating multiple data sources, including extensive in-situ PM2.5 measurements, visibility, satellite retrievals, surface and upper-level meteorological data and other ancillary data. The CLAP_PM2.5 dataset is more reliable and accurate than other public datasets. Analysis of CLAP_PM2.5 from 2010 to 2022 reveals the decrease in positive urban-nonurban PM2.5 differences and higher decreasing rates of PM2.5 in most city clusters in eastern China. Furthermore, separating meteorological and emission contributions to the PM2.5 variability by a meteorological normalization approach indicates that meteorological contribution gradually changed from unfavorable to PM2.5 reduction during 2013–2017 to favorable to decline enhancement during 2018–2022, and in urban regions, meteorological contribution is higher than that in nonurban areas. Overall, the reduction in deweathered PM2.5 concentrations highlights China's significant achievements in terms of comprehensive clean air actions.</p

Identifying Ammonia Hotspots in China Using a National Observation Network

The limited availability of ammonia (NH₃) measurements is currently a barrier to understanding the vital role of NH₃ in secondary aerosol formation during haze pollution events and prevents a full assessment of the atmospheric deposition of reactive nitrogen. The observational gaps motivated us to design this study to investigate the spatial distributions and seasonal variations in atmospheric NH₃ on a national scale in China. On the basis of a 1-year observational campaign at 53 sites with uniform protocols, we confirm that abundant concentrations of NH₃ [1 to 23.9 μg m^–3] were identified in typical agricultural regions, especially over the North China Plain (NCP). The spatial pattern of the NH₃ surface concentration was generally similar to those of the satellite column concentrations as well as a bottom-up agriculture NH₃ emission inventory. However, the observed NH₃ concentrations at urban and desert sites were comparable with those from agricultural sites and 2–3 times those of mountainous/forest/grassland/waterbody sites. We also found that NH₃ deposition fluxes at urban sites account for only half of the emissions in the NCP, suggesting the transport of urban NH₃ emissions to downwind areas. This finding provides policy makers with insights into the potential mitigation of nonagricultural NH₃ sources in developed regions