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Air quality monitoring is effective for timely understanding of the current air quality status of a region or city. Currently, the huge volume of environmental monitoring data, which has reasonable real-time performance, provides strong support for in-depth analysis of air pollution characteristics and causes. However, in the era of big data, to meet current demands for fine management of the atmospheric environment, it is important to explore the characteristics and causes of air pollution from multiple aspects for comprehensive and scientific evaluation of air quality. This study reviewed and summarized air quality evaluation methods on the basis of environmental monitoring data statistics during the 13th Five-Year Plan period, and evaluated the level of air pollution in the Beijing–Tianjin–Hebei region and its surrounding areas (i.e., the "2+26" region) during the period of the three-year action plan to fight air pollution. We suggest that air quality should be comprehensively, deeply, and scientifically evaluated from the aspects of air pollution characteristics, causes, and influences of meteorological conditions and anthropogenic emissions. It is also suggested that a three-year moving average be introduced as one of the evaluation indexes of long-term change of pollutants. Additionally, both temporal and spatial differences should be considered when removing confounding meteorological factors. [Display omitted] [ABSTRACT FROM AUTHOR]

Unsurprisingly, the amount of reactive nitrogen circulating annually on land has been doubled because of increasing anthropogenic activities. Exceedingly large amounts of reactive nitrogen (N r ) are likely to disrupt N dynamics and negatively impact the environment and human health. Guizhou Province, a major energy-producing province in southwest China, is suffering from serious long-term acid deposition. However, little work has been done to quantify the levels of atmospheric N deposition in this province, in which some ecologically vulnerable areas have resulted from rocky desertification. In this study, tissue N contents and δ 15 N signatures in 109 epilithic mosses were analyzed by the ordinary kriging (OK) interpolation technique to determine atmospheric N deposition. Moss N content (1.36–2.65%) showed a significant decrease from west to east, indicating that the spatial variance of TN deposition was the same as that of moss N content, with an average of 27.74 kg N ha −1 yr −1 . Moss δ 15 N ranged from −5.89‰ to −0.72‰ and showed an opposite spatial variance compared with moss N contents. Negative δ 15 N indicated that the main sources for N deposition were urban sewage and agricultural NH 3 . According to Moss δ 15 N values, it could be concluded that NH 4 + -N and NO 3 − -N were the main components of wet deposition, accounting for 52% and 44% of TN, respectively. The deposition fluxes were 14.49 kg N ha −1 yr −1 and 12.16 kg N ha −1 yr −1 , respectively. Although the emission flux of NO 3 − -N far exceeded that of NH 4 + -N, the amount of NH 4 + -N deposited on land was larger than that of NO 3 − -N. N deposition in 99.6% of the province exceeded the critical load for terrestrial ecosystems. High N deposition is the main environmental problem facing Guizhou Province, and recommendations regarding regulatory strategies for mitigating atmospheric N pollution are urgently needed. [ABSTRACT FROM AUTHOR]

In recent years, implementation of aggressive and strict clean air policies has resulted in significant decline in observed PM 2.5 concentration in the Beijing–Tianjin–Hebei (BTH) region and its surrounding areas (i.e., the "2 + 26" region). To eliminate the effects of interannual and seasonal meteorological variation, and to evaluate the effectiveness of emission abatement policies, we applied a boosted regression tree model to remove confounding meteorological factors. Results showed that the annual average PM2.5 concentration normalized by meteorology for the "2 + 26" region declined by 38% during 2014–2019 (i.e., from 96 to 60 μg/m3); however, the BTH region exhibited the most remarkable decrease in PM 2.5 concentration (i.e., a 60% reduction). Certain seasonal trend in normalized PM 2.5 level remained for four target subregions owing to the effects of anthropogenic emissions in autumn and winter. Although strong interannual variations of meteorological conditions were unfavorable for pollutant dispersion during the heating seasons of 2016–2018, the aggressive abatement policies were estimated to have contributed to reductions in normalized PM 2.5 concentration of 19%, 10%, 19%, and 17% in the BTH, Henan, Shandong, and Shanxi subregions, respectively. Our study eliminated the meteorological contribution to concentration variation and confirmed the effectiveness of the implemented clean air policies. Image 1 • Meteorological normalization of PM 2.5 concentration was conducted by a BRT model. • The normalized PM 2.5 concentration decreased significantly from 2014 to 2019. • Certain seasonal variations still remained in normalized PM 2.5 level. • Emission abatement policies have played a major role in reducing PM 2.5 levels. Due to aggressive and strict emission abatement policies, PM 2.5 concentrations decreased significantly year-on-year after removal of the meteorological effects. [ABSTRACT FROM AUTHOR]

Nitrogen (N) concentrations and δ 15 N signatures in soil and camphor ( Cinnamomum Camphora ) and Masson pine ( Pinus massoniana Lamb.) leaves collected along an urban-rural gradient in Guiyang (SW China) were investigated systematically. N concentrations in camphor (1.01–2.37%) and Masson pine (0.99–2.42%) leaves showed a significant decrease from central Guiyang (0–6 km) to suburban areas (18–24 km), while slightly increased leaf N concentrations reemerged at areas more than 24 km from the city center. The δ 15 N values in camphor and Masson pine leaves also decreased from central Guiyang to the rural area, with more positive leaf δ 15 N in the urban area and 15 N-depleted leaf δ 15 N in the rural area. No significant differences were observed for soil N concentrations and soil δ 15 N in these areas, which suggested that the decrease in leaf N concentrations was due to decreased atmospheric N deposition along the urban-rural gradient and that there were two isotopically different atmospheric N sources in Guiyang city: foliar δ 15 N values in urban areas were mainly influenced by 15 N-enriched atmospheric NO x -N from traffic emissions, while those in rural areas were primarily affected by 15 N-depleted atmospheric NH x -N from agricultural activities. However, the pattern of moss (collected ten years prior, with lower traffic density and wastewater treatment rate in the urban area) δ 15 N variation in the urban area (0–12 km) was contrary to that of the camphor and Masson pine leaves, indicating that the δ 15 N values in previously collected urban mosses were mainly controlled by isotopically light NH x -N from untreated wastes and sewage, but were much less affected by traffic. For the trees in the urban area, N concentrations in camphor and Masson pine leaves varied in parallel with their δ 15 N values ( P < 0.0001), and we thus applied a mass balance equation to estimate the δ 15 N value (about 7‰) in the atmospheric N deposition in the urban area. This indicated that the greater δ 15 N in urban camphor and Masson pine leaves reflected a higher contribution of NO x -N to N deposition. This study shows that the analysis of N and δ 15 N in camphor and Masson pine leaves is a promising method to indicate N deposition. [ABSTRACT FROM AUTHOR]

Particulate ammonium (NH 4 +) is one of the most important inorganic components in aerosol. The concentrations of NH 4 + in PM 2.5 significantly increased when PM 2.5 levels elevated. Increased understanding of the atmospheric processes and sources of ambient ammonia is an effective way to control atmospheric ammonia and tackle air pollution problems. This study focused on the concentration and nitrogen stable isotopic composition of particulate NH 4 + in PM 2.5 in a southwest typical plateau city, Kunming. The trend in NH 4 +concentrations was parallel to the trend in PM 2.5 levels, with obviously increased concentrations observed in November. Aerosol pH and liquid water content (ALWC) were synchronously simulated by the ISORROPIA-II model. And the ammonia gas-particle conversion ratio (f) was calculated for each day. Then, we proposed that a self-amplifying feedback mechanism of NH 4 + formation was associated with the variations of ALWC, pH, and the ammonia gas-particle conversion ratio. Based on the inverse analysis of the nitrogen isotopic composition of particulate NH 4 +, the corresponding δ15N values of initial ambient NH 3 were estimated to be −27.4‰–15.3‰, with an average of −8.1 ± 8.3‰. Results from Back trajectory analysis, PSCF analysis, and isotope-based source apportionment of NH 3 shed light on source compositions and potential source regions, indicating that, in the study area, ambient NH 3 during slightly polluted days were dominated by biomass burning emissions, which might have been originated from local emissions and regional transport process in late autumn. [Display omitted] • A self-amplifying loop was proposed when the concentration of NH 4 + in PM 2.5 elevated in late autumn in Kunming. • Biomass burning related ammonia emissions significantly enhanced during slightly polluted days. • Increased biomass burning emissions in Kunming were related to ammonia emissions from local area and regional transport. [ABSTRACT FROM AUTHOR]

Kunming, a Chinese southwestern tourist city which has not large local pollution sources, has found to have an increasing tendency of haze pollution in recent years. But the pollution sources are unclear. In order to identify them, daily PM 2.5 samples (n = 346) were collected from September 2017 to August 2018 in the urban area. And the major water-soluble inorganic ions (WSIIs) were determined to better understand the chemical characteristics, source categories and potential region of sources. Our study showed that the mass concentration of PM 2.5 in Kunming ranged from 7.61 to 91.83 μg m−3, with an annual average value of 33.59 ± 15.71 μg m−3. Positive matrix factorization (PMF) model identified five factors including secondary aerosol (the contributions of 36.3%), coal combustion (26.0%), biomass burning (19.2%), dust (12.5%) and sea salt (6.0%). And coal combustion played a leading role in the source contribution of PM 2.5 in winter while biomass combustion was dominant in spring. Being located between two severe haze zones in the world, northern-central China and north of South Asia, and affected by India monsoon and East Asia monsoon in summer and prevailing westerlies in winter, we found that air masses from South Asia (especially India) contained pollutants could be brought to Kunming by prevailing westerlies in winter. In spring, however, the sources of PM 2.5 in Kunming were mainly affected by biomass burning from South Asia and Southeast Asia when prevailing westerlies gradually weakened. Image 1 • PM 2.5 and its major water-soluble inorganic ions were characterized in Kunming. • Five source factors were identified for PM 2.5 by PMF. • Coal combustion played a leading role in the source contribution of PM 2.5 in winter. • In winter, air pollutants from India could be brought to Kunming by prevailing westerlies. • In spring, the sources of PM 2.5 were mainly affected by biomass burning from South Asia and Southeast Asia. [ABSTRACT FROM AUTHOR]