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In order to evaluate the positive and negative artifacts in the measurements of the water-soluble organic nitrogen (WSON) in the aerosols by filter sampling, comparative experiments between the filter sampling and denuder-filter sampling were conducted during both the warm and cold seasons. The results suggest that the traditional filter sampling underestimates the concentrations of the particulate WSON due to its volatilization loss, but this effect on the ratio of the WSON to the water-soluble total nitrogen (WSTN) was small probably because inorganic nitrogen species were also lost during the filter sampling. Approximately 32.5% of the WSON in the PM 2.5 was estimated to be lost during the filter sampling. The denuder–filter sampling also demonstrated the existence of the WSON in the gas phase with approximately quarter concentrations of the WSON in the PM 2.5 . On the other hand, the filter sampling would overestimate the gaseous WSON concentration due to the loss of the WSON from the aerosol collection filter. [ABSTRACT FROM AUTHOR]

A wide variety of studies have revealed a substantial increase in nitrogen (N) deposition in China, but the lack of spatially-explicit time-series N deposition data set has long hindered us from assessing the impacts of atmospheric N input on ecosystem services. In this study, we combined site-level monitoring, gridded precipitation data and atmospheric transport modeling results to generate annual N bulk deposition data in China with a spatial resolution of 10 km × 10 km and a time span from 1961 to 2008. It shows that national average N deposition rate had large interannual variation, and it increased by 59%, from 12.64 kg N ha −1 yr −1 in the 1960s to 20.07 kg N ha −1 yr −1 in the recent decade, with the most rapid increase centered in the southeastern China that is already N-enriched. Large spatial variation as well as dry deposition input has to be taken into account when estimating the amount of N deposited onto land surface of China. The spatial and temporal information on N deposition derived from this study could be used by ecosystem, hydrological, and climate modeling as well as by policy makers for assessing the impacts of nitrogen enrichment on regional climate, water resources, and biogeochemical cycles. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition has been considered as one of the important factors contributing to the critical impacts on nature, including eutrophication and biodiversity loss. To understand the effect of anthropogenic N emissions on urban-scale dry and wet N depositions, an investigation using a chemical transport model coupled with a sensitivity analysis solver was conducted in the domains that hold large megacities in Japan, the Tokyo metropolitan area, and Osaka, in the whole year of 2017. The validation results from the comparison of the modeling results to the observed results of N depositions showed that the overall calculated results replicated the observed results in the same order of magnitude. The results of the whole year calculation showed that both dry and wet N depositions were higher in spring and summer, mainly due to the higher emission of ammonia (NH 3) due to the higher temperatures in those seasons. The results of the sensitivity analysis showed that NH 3 was the most critical anthropogenic emission to the urban-scale N depositions, revealing the importance of the strategy to mitigate NH 3 reduction. The findings of this study provide a basic understanding of urban-scale N deposition in terms of atmospheric chemistry and anthropogenic emission of N compounds. [Display omitted] • An urban-scale analysis of nitrogen (N) deposition in Japan was conducted using CMAQ. • Calculated N depositions replicate the observed data in the same order of magnitude. • N deposition was high in spring and summer because of the high volatility of NH 3. • The sensitivity of NH 3 emissions to N depositions was 100 times higher than that of NO x. • NH 3 reduction is the key approach to mitigate urban-scale N deposition in Japan. [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]

Declining ammonia emissions are not always reflected in ammonia concentrations due to physicochemical processes and meteorology. Here we present a trend analysis of reduced nitrogen components over the Netherlands using two different types of atmospheric transport models: the Eulerian grid model EMEP/MSC-W and the plume model OPS. We employ calculations with the Eulerian grid model EMEP/MSC-W for the Netherlands in its EMEP4NL configuration. Using the Weather Research Forecast (WRF) model as meteorological driver plus detailed emission data over the Netherlands as input into the EMEP4NL model, we present simulation results over the Netherlands of reduced nitrogen components from this model at a horizontal resolution of 1.3 × 2.1 km. Using this configuration of the EMEP/MSC-W model (EMEP4NL), a trend analysis is performed over the period 2006–2015 for concentration and deposition of reduced nitrogen components over the Netherlands. The same analysis is performed with the OPS-model, a plume model with a Lagrangian trajectory model for long range transport. Both models use the same MACC III emission distribution for countries outside of the Netherlands, and spatially more detailed emissions for the Netherlands itself. Emission totals per SNAP (Supporting National Action and Planning) sector per country are used over the period 2006–2015, according to the latest CEIP (Centre on Emissions Inventories and Projections) expert estimates. The OPS-model is driven with yearly specific meteorological fields provided by the Royal Netherlands Meteorological Institute (KNMI). Furthermore, the OPS-model parameterizes its chemistry, whereas EMEP4NL uses a state-of-the-art chemistry scheme. Results from ammonia concentrations, ammonium concentrations and wet deposition as calculated with both models, are first compared with observations from the National Air Quality Monitoring Network in the Netherland (LML). Calculations of ammonia and wet deposition both agree well with the measurements in the OPS and the EMEP4NL model. Ammonium is better represented by calculations with the EMEP4NL model than by the OPS-model. Measurements of dry deposition of reduced nitrogen are very limited, therefore only a comparison is made between the model results of EMEP4NL and OPS. Subsequently, a trend analysis is performed over the period 2006–2015 for the reduced nitrogen components for both model calculation results and the measurements. The trends of all components are calculated over the mean values of monitoring stations over the Netherlands. The reported decline in the emissions of ammonia is not reflected in the ammonia concentrations and wet deposition of reduced nitrogen as measured and calculated with the OPS and the EMEP4NL model. Ammonium concentrations on the other hand are declining (also) due to the decrease of the SO x emissions over the period 2006–2015. Finally, both models show a slight decline in the dry deposition values, despite the fact that both models (and observations) do not show a decrease in the ammonia concentrations. A more detailed analysis of the comparison of dry deposition of reduced nitrogen between both models, and the influence of the physicochemical processes and meteorology is in preparation. Overall, it is found that the calculated trends for the different reduced nitrogen components with a grid model like EMEP4NL and a plume model like OPS are roughly in line with each other. • A plume and a grid model are used to model air pollution and deposition of reduced nitrogen over a period of 10 years. • The two models used have different basic calculation techniques plus a different treatment of the atmospheric chemistry and large-scale transport. • An overall good agreement is found between calculations and measurements of the reduced nitrogen components. • The temporal trends of the different reduced nitrogen components in models and measurements are also in rough agreement. [ABSTRACT FROM AUTHOR]