Flue gas desulfurization (FGD) and selective catalytic reduction (SCR) technologies have been widely used to control the emissions of sulphur dioxide (SO2) and nitrogen oxides (NOX) from coal-fired power plants (CFPPs). Field measurements of emission characteristics of four conventional CFPPs indicated a significant increase in particulate ionic species, increasing PM2.5 emission with FGD and SCR installations. The mean concentrations of PM2.5 from all CFPPs tested were 3.79 ± 1.37 mg/m3 and 5.02 ± 1.73 mg/m3 at the FGD inlet and outlet, respectively, and the corresponding contributions of ionic species were 19.1 ± 7.7% and 38.2 ± 7.8%, respectively. The FGD was found to enhance the conversion of NH3 slip from the SCR to NH4+ in the PM2.5, together with the conversion of SO2 to SO42-, and increased the primary NH4+ and SO42- aerosol emissions by approximately 18.9 and 4.2 times, respectively. This adverse effect should be considered when updating the emission inventory of CFPPs and should draw the attention of policy-makers for future air pollution control.

Fine particle (PM2.5) samples were collected simultaneously at three urban sites (Shanghai, Nanjing, and Hangzhou) and one rural site near Ningbo in the Yangtze River Delta (YRD) region, China, on a weekly basis from September 2013 to August 2014. In addition, high-frequency daily sampling was conducted in Shanghai and Nanjing for one month during each season. Severe regional PM2.5 pollution episodes were frequently observed in the YRD, with annual mean concentrations of 94.6 ± 55.9, 97.8 ± 40.5, 134 ± 54.3, and 94.0 ± 57.6 μg m−3 in Shanghai, Nanjing, Hangzhou, and Ningbo, respectively. The concentrations of PM2.5 and ambient trace metals at the four sites showed clear seasonal trends, with higher concentrations in winter and lower concentrations in summer. In Shanghai, similar seasonal patterns were found for organic carbon (OC), elemental carbon (EC), and water-soluble inorganic ions (K+, NH4+, Cl−, NO3−, and SO42-). Air mass backward trajectory and potential source contribution function (PSCF) analyses implied that areas of central and northern China contributed significantly to the concentration and chemical compositions of PM2.5 in Shanghai during winter. Three heavy pollution events in Shanghai were observed during autumn and winter. The modelling results of the Nested Air Quality Prediction Modeling System (NAQPMS) showed the sources and transport of PM2.5 in the YRD during the three pollution processes. The contribution of secondary species (SOC, NH4+, NO3−, and SO42-) in pollution event (PE) periods was much higher than in BPE (before pollution event) and APE (after pollution event) periods, suggesting the importance of secondary aerosol formation during the three pollution events. Furthermore, the bioavailability of Cu, and Zn in the wintertime PM2.5 samples from Shanghai was much higher during the pollution days than during the non-pollution days.

To investigate the size distributions of chemical compositions and sources of particulate matter (PM) at ground level and from the urban canopy, a study was conducted on a 255 m meteorological tower in Tianjin from December 2013 to January 2014. Thirteen sets of 8 size-segregated particles were collected with cascade impactor at 10 m and 220 m. Twelve components of particles, including water-soluble inorganic ions and carbonaceous species, were analyzed and used to apportion the sources of PM with positive matrix factorization. Our results indicated that the concentrations, size distributions of chemical compositions and sources of PM at the urban canopy were affected by regional transport due to a stable layer approximately 200 m and higher wind speed at 220 m. The concentrations of PM, Cl− and elemental carbon (EC) in fine particles at 10 m were higher than that at 220 m, while the reverse was true for NO3− and SO42−. The concentrations of Na+, Ca2+, Mg2+, Cl− and EC in coarse particles at 10 m were higher than that at 220 m. The size distributions of major primary species, such as Cl−, Na+, Ca2+, Mg2+ and EC, were similar at two different heights, indicating that there were common and dominant sources. The peaks of SO42−, NH4+, NO3− and organic carbon (OC), which were partly secondary generated species, shifted slightly to the smaller particles at 220 m, indicating that there was a different formation mechanism. Industrial pollution and coal combustion, re-suspended dust and marine salt, traffic emissions and transport, and secondary inorganic aerosols were the major sources of PM at both heights. With the increase in vertical height, the influence of traffic emissions, re-suspended dust and biomass burning on PM weakened, but the characteristics of regional transport from Hebei Province and Beijing gradually become obvious.

The quantification of atmospheric deposition flux is essential for assessment of its impact on ecosystems. We present an advanced approach for the estimation of the spatial pattern of atmospheric nitrogen deposition flux over the Czech forests, collating all available measured data and model results. The aim of the presented study is to provide an improved, more complete, more reliable and more realistic estimate of the spatial pattern of nitrogen deposition flux over one country. This has so far usually been based on measurements of ambient NOx concentrations as dry deposition proxy, and NH4+ and NO3− in precipitation as wet deposition proxy. For estimation of unmeasured species contributing to dry deposition, we used the CAMx Eulerian photochemical dispersion model, coupled with the Aladin regional numeric weather prediction model. The contribution of fog and dissolved organic nitrogen was estimated using a geostatistical data driven model. We prepared individual maps for particular components applying the most relevant approach and then merged all layers to obtain a final map representing the best estimate of nitrogen deposition over the Czech Republic. Final maps accounting for unmeasured species clearly indicate that the approach used so far may result in a substantial underestimation of nitrogen deposition flux. Our results showed that nitrogen deposition over the Czech forested area in 2008 was well above 2 g N m−2 yr−1, with almost 70% of forested area receiving 3–4 g N m−2 yr−1. NH3 and gaseous HNO3, contributing about 80%, dominated the dry nitrogen deposition. Estimating the unmeasured nitrogen species by modeled values provides realistic approximations of total nitrogen deposition that also result in more realistic spatial patterns that could be used as input for further studies of likely nitrogen impacts on ecosystems.

A survey of 153 acid grasslands from the Atlantic biogeographic region of Europe indicates that chronic nitrogen deposition is changing plant species composition and soil and plant-tissue chemistry. Across the deposition gradient (2–44 kg N ha⁻¹ yr⁻¹) grass richness as a proportion of total species richness increased whereas forb richness decreased. Soil C:N ratio increased, but soil extractable nitrate and ammonium concentrations did not show any relationship with nitrogen deposition. The above-ground tissue nitrogen contents of three plant species were examined: Agrostis capillaris (grass), Galium saxatile (forb) and Rhytidiadelphus squarrosus (bryophyte). The tissue nitrogen content of neither vascular plant species showed any relationship with nitrogen deposition, but there was a weak positive relationship between R. squarrosus nitrogen content and nitrogen deposition. None of the species showed strong relationships between above-ground tissue N:P or C:N and nitrogen deposition, indicating that they are not good indicators of deposition rate.

To assess pollution levels of major inorganic nitrogen species and their atmospheric deposition input to sensitive ecosystems in Sichuan Basin, southwest China, ambient concentrations of oxidized (NOy ∼ NO2, HNO3, NO3−) and reduced (NHx = NH3, NH4+) nitrogen species were collected at two urban sites during four one-month periods, each in a different season from July 2014 to April 2015. Estimated annual mean concentration of NOy was 20.3 and 13.5 μg N m−3 in Chengdu and Wanzhou, respectively, and NHx was 16.9 and 13.6 μg N m−3, respectively. Back trajectory cluster analysis indicated that high levels of NOy and NHx in Chengdu were mainly caused by local emissions while those in Wanzhou were caused by both the local emissions and long-range transport of pollutants. On annual basis, NO2 contributed the most to NOy, followed by NO3− and HNO3, accounting for 87.5%, 10.5% and 2.0%, respectively, of NOy in Chengdu, and 91.4%, 6.9% and 1.7%, respectively, in Wanzhou. NH3 was the predominant contributor to NHx, contributing 65.6% and 72.2% in Chengdu and Wanzhou, respectively. Dry deposition fluxes were estimated using the inferential method with measured ambient concentrations and modelled dry deposition velocities. The total inorganic nitrogen dry deposition flux was estimated to be 21.4 and 8.5 kg N ha−1 yr−1, with 44.3% and 41.4% from NOy in Chengdu and Wanzhou, respectively. NO2 and NH3 each contributed about 80% of NOy and NHx dry deposition, respectively. Wet deposition was only collected in Wanzhou, where the annual wet deposition of NO3− and NH4+ was 4.5 and 15.7 kg N ha−1 yr−1, respectively. The total wet plus dry deposition was 28.7 kg N ha−1 yr−1 in Wanzhou with 72.2% from reduced nitrogen. Therefore, controlling NH3 emissions from agricultural, traffic, waste containers and sewage system sources would be effective to reduce the total nitrogen deposition in the Sichuan Basin area.

Size-segregated particulate pollutants (PM<0.95, PM0.95–1.5, PM1.5–3.0, PM3.0–7.2 and PM>7.2) were collected over Patiala (30.33°N, 76.40°E; 250 m amsl), a semi-urban city located in northwestern Indo-Gangetic Plain (IGP), during October, 2012 to September, 2013. Mass concentration of total suspended particulates (TSP), derived by summation of particulate (aerosol) mass in different size range, varied from 88 to 387 μg m−3 with highest mass concentration (∼55% of total mass) in submicron size (PM<0.95) during the entire study period, which broadly reflects relative higher contribution of various anthropogenic sources (emissions from biomass and bio-fuel burning, vehicles, thermal power plants, etc) to ambient particles. Concentration of SO42−, NO3−, NH4+, K+ and Ca2+ exhibited large variability ranging from 0.52 to 40, 0.20 to 19, 0.14 to 12, 0.06 to 5.3 and 0.08 to 5.6 μg m−3, respectively, in different size ranges with varying size distribution for most of the species, except NH4+. A strong linear correlation (r = 0.97) between (SO42− + NO3−) and (K+ + NH4+) concentrations has been observed in submicron particles collected in different seasons, suggesting the formation of secondary inorganic salts. However, relatively poor correlation is observed in higher size ranges where significant correlation between (SO42− + NO3−) and (Ca2+ + Mg2+) has been observed. These observations indicate the acid neutralization by dust in coarser modes of particles. Chemical composition of submicron particulates (PM<0.95) in different seasons as well as for whole year was used to identify PM sources through the application of Positive Matrix Factorization (PMF, version 5.0) model. Based on annual data, PMF analyses suggests that six source factors namely biomass burning emission (24%), vehicular emission (22%), secondary organic aerosols (20%), power plant emission (13%), secondary inorganic aerosols (12%) and mineral dust (9%) contribute to PM<0.95 loading over the study region. Such studies are important in dispersion modeling, health impact assessment, and planning of pollution mitigation strategies.

Hydrochemical sampling of South Pennine (UK) headwater streams draining eroded upland peatlands demonstrates these systems are nitrogen saturated, with significant leaching of dissolved inorganic nitrogen (DIN), particularly ammonium, during both stormflow and baseflow conditions. DIN leaching at sub-catchment scale is controlled by geomorphological context; in catchments with low gully densities ammonium leaching dominates whereas highly gullied catchments leach ammonium and nitrate since lower water tables and increased aeration encourages nitrification. Stormflow flux calculations indicate that: approximately equivalent amounts of nitrate are deposited and exported; ammonium export significantly exceeds atmospheric inputs. This suggests two ammonium sources: high atmospheric loadings; and mineralisation of organic nitrogen stored in peat. Downstream trends indicate rapid transformation of leached ammonium into nitrate. It is important that low-order headwater streams are adequately considered when assessing impacts of atmospheric loads on the hydrochemistry of stream networks, especially with respect to erosion, climate change and reduced precipitation.

Acid rain is a serious environmental problem in China, caused by the urbanization and industrialization. We used recent acid rain and urban pollutant emissions data from the eastern coastal Jiangsu province to analyze the spatial distribution of acid rain. Further, we analyzed the regional air pollution data of the commission discharge atmospheric research database (EDGAR) regional air pollution data and developed a back-trajectory model for the cluster analysis of the air mass transfer characteristics of acid rain. The results show that from 2007 to 2013 the precipitation pH were high in northern and low in southern parts of Jiangsu Province. The average precipitation pH in the northwest and northeast parts were higher than 5.6; the frequency of acid rain in the area south of the Huaihe River accounted for more than 50% of total rainfall samples. Precipitation conductive in the northwest and southwest was greater than 60 μs/cm. The SO2, NOX, and PM10 were lower in the northern part and higher in the southern part. The northern part has higher pH and lower emission of precursors. One likely source for high ammonium and calcium concentration is local soil. From the northwest air mass, the acid rain appeared to have the highest average pH and the air mass from the southwest had the highest percentage of acid rain. The local emission (SO2, NOX, and Dust) reduction from 2005 led the haze and the acid rain problems mitigated to a good trend. The haze day increase and acid rain decrease due to the NH4+, and Ca2+ increase, and the long-distance transmission and the alkaline pollutant played an important role in Jiangsu' acid rain problem and haze since 2009.

Here we characterized wet deposition National Atmospheric Deposition Program (NADP) species and Clean Air Status and Trends Network (CASTNET) dry deposited particle and gas species across New York over the last 2-3 decades. In addition measurements of NH3 from the Ammonia Monitoring Network (AMoN) were analyzed. In general decreasing annual trends are observed for wet deposition SO42− and NO3− species and dry deposited particle SO42−, NO3− and NH4+ as well as gas phase SO2 and HNO3 consistent with reductions in SO2 and NOx emissions. Wet deposited NH4+ however does not show consistent trends with most sites showing little trend across the region and an indication that levels at some sites maybe increasing. NH3 concentrations also appear to be increasing although the data record is only 8 years. Base cations, Ca2+ and Mg2+ show some decreases in the 1980s but concentrations are relatively uniform since the mid-1990s. Na+ and K+ show large year to year variations, by more than an order of magnitude for Na+ due to influence of marine air at a near coastal site. In general there was a balance between the sum of cations and the sum of anions earlier in the record but the tendency has been for a cation excess in the more recent 5–10 years. Understanding the deposition of reduced nitrogen species is likely to be of concern for the foreseeable future. Such data are important in understanding acidification recovery in response to emission controls.