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NOx
About: NOx is a research topic. Over the lifetime, 26367 publications have been published within this topic receiving 496555 citations.
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TL;DR: In this article, a consistent association was found between the sensitivity of ozone to reductions in ROG versus NOx emissions and the simulated total reactive nitrogen (NOy) at the time and place of peak ozone.
Abstract: For areas in the United States not meeting the federal air quality standard for ozone, an issue of continuing controversy is the emphasis to be placed on controlling nitrogen oxides (NOx) in addition to emissions of reactive organic gases (ROG). To assess conditions under which ROG or NOx controls would be most effective, we have analyzed predictions from four studies that represent different locations and meteorological conditions, distinct chemical inputs, e.g., with or without significant biogenic emissions, and different air quality models. A consistent association is found between the sensitivity of ozone to reductions in ROG versus NOx emissions and the simulated total reactive nitrogen (NOy) at the time and place of peak ozone. In the studies examined, ozone was predicted to be reduced most effectively by ROG controls at locations where NOy concentrations exceeded a threshhold value falling in the range of 10 to 25 ppb, whereas NOx controls were predicted to be more effective where NOy concentrations were below that threshhold. The NOy level explains much of the difference in ozone sensitivity at different locations and provides a basis for comparison of predicted sensitivity from different models. In contrast, the morning concentration ratio of ROG to NOx that has been used in the past is a less reliable indicator of O3 sensitivity. Measurement of NOy concentrations along with ozone would assist in empirical testing of model predictions of responses to emission reductions.
183 citations
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TL;DR: In this article, the first direct measurements of nitrogen dioxide (NO2) in the UK using a vehicle emission remote sensing technique were made spanning vehicle model years from 1985 to 2012, and the results showed that only petrol fuelled vehicles have shown an appreciable reduction in total NOx emissions over the past 15e20 years.
182 citations
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TL;DR: A comprehensive assessment of ammonia (NH(3), nitrogen oxides (NO(x), and nitrous oxide (N(2)O) emissions in China based on a full cycle analysis provides policy makers an integrated view of Nr sources and health damage to address the significant challenges associated with the reduction of air pollution.
Abstract: Human activities have intensely altered the global nitrogen cycle and produced nitrogenous gases of environmental significance, especially in China where the most serious atmospheric nitrogen pollution worldwide exists. We present a comprehensive assessment of ammonia (NH3), nitrogen oxides (NOx), and nitrous oxide (N2O) emissions in China based on a full cycle analysis. Total reactive nitrogen (Nr) emission more than doubled over the past three decades, during which the trend of increase slowed for NH3 emissions after 2000, while the trend of increase continued to accelerate for NOx and N2O emissions. Several hotspots were identified, and their Nr emissions were about 10 times higher than others. Agricultural sources take 95% of total NH3 emission; fossil fuel combustion accounts for 96% of total NOx emission; agricultural (51%) and natural sources (forest and surface water, 39%) both contribute to the N2O emission in China. Total atmospheric Nr emissions related health damage in 2008 in China reached US...
182 citations
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TL;DR: In this paper, a three-dimensional, continental-scale photochemical model is used to investigate seasonal budgets of 03 and NO3 species in the boundary layer over the United States and to estimate the export of these species from the U.S. boundary layer to the global atmosphere.
Abstract: A three-dimensional, continental-scale photochemical model is used to investigate seasonal budgets of 03 and NO3. species (including NOx and its oxidation products) in the boundary layer over the United States and to estimate the export of these species from the U.S. boundary layer to the global atmosphere. Model results are evaluated with year-round observations for 03, CO, and NO, species at nonurban sites. A seasonal transition from NO, to hydrocarbon-limited conditions for 03 production over the eastern United States is found to take place in the fall, with the reverse transition taking place in the spring. The mean NOx/NOy molar ratio in the U.S. boundary layer in the model ranges from 0.2 in summer to 0.6 in winter, in accord with observations, and reflecting largely the seasonal variation in the chemical lifetime of NOx. Formation of hydroxy organic nitrates during oxidation of isoprene, followed by decomposition of these nitrates to HNO 3, is estimated to account for 30% of the chemical sink of NOx in the U.S. boundary layer in summer. Model results indicate that peroxyacylnitrates (PANs) are most abundant in the U.S. boundary layer in spring (25% of total NO3.), reflecting a combination of active photochemistry and low temperatures. About 20% of the NOx emitted from fossil fuel combustion in the United States in the model is exported out of the U.S. boundary layer as NOx or PANs (15% in summer, 25% in winter). This export responds less than proportionally to changes in NOx emissions in summer, but more than proportionally in winter. The annual mean export of NOx and PANs from the U.S. boundary layer is estimated to be 1.4 Tg N yr - , representing an important source of NOx on the scale of the northern hemisphere troposphere. The eventual 03 production in the global troposphere due to the exported NOx and PANs is estimated to be twice as large, on an annual basis, as the direct export of 03 pollution from the U.S. boundary layer. Fossil fuel combustion in the United States is estimated to account for about 10% of the total source of 03 in the northern hemisphere troposphere on an annual basis.
182 citations
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TL;DR: In this paper, the characteristics of moderate or intense lowoxygen dilution (MILD) oxy-combustion in a laboratory-scale furnace were investigated for a range of equivalence ratios and external-CO2 dilution rates.
182 citations