Ratio Of NO Research Articles

Separately resolving NOx and VOC contributions to ozone formation

Ozone (O3) is widely recognized as a significant air pollutant that affects public health across the globe. O3 is formed from precursor emissions of oxides of nitrogen (NOx) and volatile organic compounds (VOCs) that react in the atmosphere, making it complex to identify the major source contributions to O3 concentrations. O3 source apportionment calculations within chemical transport models (CTMs) provide a specialized approach to resolve source contributions. Traditional O3 apportionment techniques track source contributions based on the chemical formation regime, but they do not separately distinguish between NOx and VOC source contributions. In this study, a new O3 source apportionment technique was developed to explicitly resolve the contributions from both NOx and VOC sources in order to provide a more detailed view on O3 source origins so that policy makers can design more effective emission control strategies. The new technique is flexible and can be configured to identify the original source of precursors that contribute to O3 formation or the most recent source depending on the choice of the tagging method. The detailed features of the new technique are demonstrated during a peak O3 event in September 2010 in Los Angeles, while trends in O3 source contributions over time are evaluated during two additional simulations in July 2005 and August 2015. Quality control checks show that the new source apportionment methodology does not alter predicted total O3 concentrations, and the detailed source apportionment information can be averaged to yield results that are consistent with traditional O3 source apportionment calculations. The detailed O3 source apportionment results during Sept 2010 show that, among NOx sources, on-road gasoline, on-road diesel, off-road diesel, and soil NOx account for over 60% of the ground level O3 concentrations. Among VOC sources, upwind boundary conditions and biogenic sources account for approximately 90% of the ground-level O3 formed. The formaldehyde to NO2 ratio suggests that the chemical regime in the year 2015 was VOC-limited, but given the uncontrollable nature of the VOC emissions, the results suggest that NOx emission controls would have been the preferred emission control strategy to reduce O3 concentration in Los Angeles at that time, with the understanding that some period of O3 disbenefits would need to be tolerated until the emissions control program shifts the atmospheric chemistry back into the NOx-limited regime. The NOx source apportionment results for O3 identify the largest NOx sources that could be reduced in an effort to reach NOx-limited conditions. The chemical regime in the Los Angeles atmosphere is continuously evolving, and so these calculations would need to be repeated under current conditions to determine if we have arrived at this NOx limited regime. Future studies will undertake this analysis.

Identifying the Sources and Drivers of Nitrous Oxide Accumulation in the Eddy‐Influenced Eastern Tropical North Pacific Oxygen‐Deficient Zone

AbstractNitrous oxide (N2O) is a powerful greenhouse gas, and oceanic sources account for up to one third of the total natural flux to the atmosphere. In oxygen‐deficient zones (ODZs) like the Eastern Tropical North Pacific (ETNP), N2O can be produced and consumed by several biological processes. In this study, the concentration and isotopocule ratios of N2O from a 2016 cruise in the ETNP were analyzed to examine sources of and controls on N2O cycling across this region. Along the north‐south transect, three distinct biogeochemical regimes were identified: background, core‐ODZ, and high‐N2O stations. Background stations were characterized by smaller variations in N2O concentration and isotopic profiles relative to the other regimes. Core‐ODZ stations were characterized by co‐occurring N2O production and consumption at anoxic depths, indicated by high δ18O‐N2O (>90‰) and low δ15N2Oβ (<−10‰) values, and confirmed by a time‐dependent model, which indicated that N2O production via denitrification was significant and may occur with a nonzero site preference. High‐N2O stations, located at the periphery of a mesoscale eddy, were defined by N2O reaching 126.07 ± 12.6 nM and low oxygen concentrations expanding into near‐surface isopycnals. At these stations, model results indicated significant N2O production from ammonia‐oxidizing archaea and denitrification from nitrate at the N2O maximum within the oxycline, while bacterial nitrification and denitrification from nitrite were insignificant. This study also represents the first in the ETNP to link N2O production mechanisms to a mesoscale eddy through isotopocule measurements, suggesting the importance of eddies to spatiotemporal variability in N2O cycling and emissions from this region.

Seasonal Variation in Chemical Composition of Total Suspended Particles During the COVID-19 Pandemic in the Source Area of Urumqi River, Tianshan, China

The research of atmospheric aerosol in mountain glacier areas has attracted more and more people’s attention. For the first time, a field observation study of total suspended particles (TSPs) for four seasons from September 2019 to August 2020 was carried out at the Tianshan Glaciological Station in the source area of Urumqi River, East Tianshan Mountains, China. The TSPs presented typical seasonal characteristics of high in autumn and low in winter, with the annual average value of 181 ± 170 μg m−3. Concentrations of Ca2+, SO42−, NO3−, Cl−, NH4+ and K+, OC, EC were elevated in autumn. The influence of stationary source emissions was stronger than mobile sources, which was explained by the average ratio of NO3−/SO42− (0.31 ± 0.17). The concentration of secondary organic carbon (SOC) was higher in summer and autumn, especially in summer, indicating that secondary formation processes of organic aerosols were frequent in summer. Impact of fossil fuel combustion sources were evident over the Glaciers, corroborated by the diagnostic mass ratios of OC/EC (0–21.4, 3.38) and K+/EC (0–0.31, 0.08). The factor analysis illustrated that aerosols were mainly affected by rock salt, dust, coal combustion, and automobile exhaust. The local sources made significant contributions to TSPs in the source of Urumqi River by the results of Results of Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and potential source contribution function (PSCF).

Non-thermal argon plasma jets of various lengths for selective reactive oxygen and nitrogen species production

Plasma jets simultaneously create a wide range of reactive oxygen species (ROS) and reactive nitrogen species (RNS), making selective production challenging. In this study, an attempt was made to address this problem by adjusting the downstream length of the plasma jet to regulate reactive species production in an AC-driven argon plasma jet. Jets with short downstream lengths are dominated by RNS, whereas longer ones are dominated by ROS. The energy impact collision between energetic electrons and diffused ambient air is primarily responsible for the generation of RNS in argon plasma. Short plasma jets have a higher electron temperature in the plasma effluent, allowing for better excitation and ionization of N2 molecules. In contrast, in longer jets, electrons transfer most of their energy to neutrals and moisture, even before the diffusion of ambient air. Thus, the production of OH radicals and H2O2 is dominant in longer plasma jets. Further, the ratio of NO2- to H2O2 in plasma-activated water decreased from 1.8 to 0.07, as the downstream length was increased from 1 cm to 10 cm. RNS-enriched short plasma jets are appropriate for immune cell activation, jets of intermediate length are suitable for gold nanoparticle formation because of the synergistic action of ROS and electron energy, and ROS-dominated longer plasma jets are excellent for methylene blue degradation. These findings are applicable to the design of plasma devices in which the generation of ROS and RNS in practical quantities is required to realize plasma technology for a wide range of applications.

Anthropogenic Influences on an Urban River: Differences in Cations and Nutrients along an Urban/Suburban Transect

The Anacostia River in Washington, D.C. has been experiencing the challenges typical of urban rivers over the last 70+ years. Here, we examine six years (2014 to 2020) of base-flow geochemistry of three tidal Anacostia sites and three suburban sites. Parameters examined include pH, hardness, SAR, alkalinity, TDS, Ca, Mg, Na, K, Fe, Mn, Zn, Al, As, B, Ba, Be, Cd, Cr, Cu, Co, Mo, Ni, Pb, total P, S, Sr, Ti, NO3−, and NH4+. Not surprisingly, winter and spring months showed very high Na (means of 786 mg/L and 1000 mg/L, respectively). Plotting Na/(Na + Ca) versus TDS shows contributions from groundwater, but also differences from major world rivers. Main stem locations usually had Ca/Sr ratios > 200, suggesting that concrete was the source of Ca; however, suburban sites showed high Ca as well and suburban Ca/Sr ratios were frequently <200, indicating a different source for Ca. Most sites showed low median Si:NO3 ratios (between 3 and 5), suggesting elevated NO3− from non-natural sources. The data are consistent with freshwater salinization syndrome (a specific type of urban stream syndrome), and also show that the developed landscape in suburban environments influences geochemistry differently than in urban environments.

Microsoft Excelのフーリエ解析を用いるノイズ信号の軽減─フローインジェクション分析法におけるシグナルノイズ比の向上─

In flow injection analysis (FIA), the baseline noise of the detection signal is an important parameter that determines the detection sensitivity. In this study, we applied the Fourier analysis/inverse Fourier analysis of Microsoft Excel to the detection signal of FIA to decrease the noise signal. The Fourier analysis of the detection signal for a sample of 0.06 mg L−1 NO2− showed many frequency components with amplitudes less than 0.04 mV. After removing these frequency components, inverse Fourier analysis was applied, and a smooth detection signal was obtained. Even with a sample of 2.50 mg L−1 NO2−, the noise signals were successfully removed using the Fourier/inverse Fourier analysis. The signal-to-noise ratio (S/N) of NO2− was improved by ca. 15 times. We concluded that removing noise signals by Fourier analysis effectively improves the S/N of FIA.

Achieving Partial Nitrification-Anammox Process Dependent on Microalgal-Bacterial Consortia in a Photosequencing Batch Reactor.

Partial nitrification coupled with anammox (PN/A) process is an energy-efficient approach for nitrogen removal from low C/N wastewater. In this study, PN/A was achieved with optimal oxygen supply from a green microalga, Chlorella sorokiniana. The PN process was first initiated within 35 days, and the following algae-intensified PN then reached the steady state within the next 32 days. The dissolved oxygen (DO) concentration was gradually maintained at 0.6 mg L−1 via adjusting the photoperiod to 6-h light/18-h dark cycles, when the accumulation ratio of NO2 −-N and the removal ratio of NH4 +-N were both more than 90%. The nitrogen removal capability of anammox was acclimated via elevating the individual effluent NH4 +-N and NO2 −-N levels from 100 to 200, to 300 mg L−1. After acclimation, the removal rates of NH4 +-N and total nitrogen (TN) reached more than 70 and 80%, respectively, and almost all the NO2 −-N was removed. Then, the algae-intensified PN/A, algammox biofilm system, was successfully started up. When the NH4 +-N level increased from 100 to 300 mg L−1, the TN removal varied between 78 and 82%. In the photosequencing bioreactor, C. sorokiniana, ammonia-oxidizing bacteria (AOB), and anammox coexisted with an illumination of 200 μmol m−2 s−1 and a 6-h light/18-h dark cycles. The DO levels ranged between 0.4 and 0.5 mg L−1. In addition, the microbial community analysis by Illumina MiSeq sequencing showed that the dominant functional bacteria in the algae-intensified PN/A reactors included Nitrosomonas (AOB) and Candidatus Brocadia (anammox), while Nitrospira and Nitrobacter (nitrite oxidizing bacteria), together with Denitratisoma (denitrifier) were largely inhibited. Further studies are required to optimize the microalgal–bacterial consortia system to achieve superior nitrogen removal rates under controllable conditions.

Submicron-scale aerosol above the city canopy in Beijing in spring based on in-situ meteorological tower measurements

Non-refractory submicron-scale aerosol (NR-PM1) chemical species above the city canopy in Beijing in spring were studied based on observations at the Beijing 325-m meteorological tower in combination with analyses of the meteorological field and mixing layer height (MLH). The parallel sampling showed that the NR-PM1 at 260 m (60 μg/m3) was ~70% of that at ground level. Organic aerosol (Org) was the species with the most significant vertical difference, as its average mass concentration at 260 m was half of that at ground level. In 91% of cases, the Org at ground level was higher than that at 260 m. Sulfate (SO4) and chloride had more regional transport characteristics. Nitrate (NO3) and Org were more enriched at ground level, as the online molar ratio of NO3 to SO4 and the mass ratio of Org to SNA (sulfate–nitrate–ammonium) were higher at ground level. Among all the five NR-PM1 chemical species, ammonium nitrate was the species with the most uniform vertical distribution. Pollution events in spring in urban Beijing were accompanied by a gradual increase in ground RH from 10% to more than 35%. Strong winds from the southwest polluted region could also maintain the NR-PM1 at a high level. The polluted air masses transported from the south accounted for 39%, which was about four times that of the clean air masses from the northwest (11%). Thus, atmospheric circulation in spring is generally conducive to the formation of pollution. The estimated dilution efficiency on NR-PM1 chemical species influenced by boundary layer variation in spring showed that, when the mix layer was elevated the dilution effect at higher altitude was stronger than that at ground level.

Satellite-Based Diagnosis and Numerical Verification of Ozone Formation Regimes over Nine Megacities in East Asia

Urban photochemical ozone (O3) formation regimes (NOx- and VOC-limited regimes) at nine megacities in East Asia were diagnosed based on near-surface O3 columns from 900 to 700 hPa, nitrogen dioxide (NO2), and formaldehyde (HCHO), which were inferred from measurements by ozone-monitoring instruments (OMI) for 2014–2018. The nine megacities included Beijing, Tianjin, Hebei, Shandong, Shanghai, Seoul, Busan, Tokyo, and Osaka. The space-borne HCHO–to–NO2 ratio (FNR) inferred from the OMI was applied to nine megacities and verified by a series of sensitivity tests of Weather Research and Forecasting model with Chemistry (WRF-Chem) simulations by halving the NOx and VOC emissions. The results showed that the satellite-based FNRs ranged from 1.20 to 2.62 and the regimes over the nine megacities were identified as almost NOx-saturated conditions, while the domain-averaged FNR in East Asia was >2. The results of WRF–Chem sensitivity modeling show that O3 increased when the NOx emissions reduced, whereas VOC emission reduction showed a significant decrease in O3, confirming the characteristics of VOC-limited conditions in all of the nine megacities. When both NOx and VOC emissions were reduced, O3 decreased in most cities, but increased in the three lowest-FNRs megacities, such as Shanghai, Seoul, and Tokyo, where weakened O3 titration caused by NOx reduction had a larger enough effect to offset O3 suppression induced by the decrease in VOCs. Our model results, therefore, indicated that the immediate VOC emission reduction is a key controlling factor to decrease megacity O3 in East Asia, and also suggested that both VOC and NOx reductions may not be of broad utility in O3 abatement in megacities and should be considered judiciously in highly NOx-saturated cities in East Asia.

Inferring vertical variability and diurnal evolution of O3 formation sensitivity based on the vertical distribution of summertime HCHO and NO2 in Guangzhou, China

The vertical distributions of formaldehyde (HCHO) and nitrogen dioxide (NO2) and their indicative roles in ozone (O3) sensitivity are important for designing O3 mitigation strategies. Using hyperspectral remote sensing observations, tropospheric vertical profiles of HCHO, NO2, and aerosol extinction were investigated in Guangzhou, China from July to September 2019. On both O3 non-exceedance and polluted days, the HCHO and aerosol vertical profiles exhibited similar Gaussian shapes, but the NO2 profile exhibited an exponential decreasing shape. HCHO and aerosol were especially sensitive to O3 pollution, with higher values generally occurring at approximately noon and late afternoon at higher altitudes. We attempted to study the diurnal evolution of O3 sensitivity at different altitudes based on the HCHO to NO2 ratio (FNR) vertical profile. The FNR thresholds marking the transition regime (2.5 < FNR < 4.0) were derived from the relationship between the increase in O3 (∆O3) and FNR. Our results showed that O3 sensitivity tends to be VOC-limited both at lower (below approximately 0.4 km) and higher (above approximately 1.8 km) altitudes throughout the daytime. In the middle altitudes, the photochemical formation of O3 was mainly in the transition/NOx-limited regime in the morning and afternoon but in the VOC-limited regime at noontime. The relationship between TROPOMI column FNR and near-surface O3 sensitivity was further investigated. Compared with the MAX-DOAS near-surface FNR, slightly higher values of column FNR would increase the number of days classified as transition regimes, which was mainly caused by the inhomogeneous vertical distribution of HCHO and NO2 in the lower troposphere. This study provides an improved understanding of vertical variability and diurnal evolution of O3 formation sensitivity.

Intense denitrification and sewage effluent result in enriched 15N in N2O from urban polluted rivers

Urban polluted rivers are important sources of N2O because they receive heavy nitrogen loads containing N2O and its precursors. Understanding the N2O budget is vital to the formulation of N2O emissions reduction policies. The isotopic ratios of N2O from different sources can provide insights into global N2O budgets. Isotopic ratios of N2O from soil and marine has been well studied, yet few studies have explored dynamics of dissolved N2O and its isotopic ratios in urban polluted rivers. In this study, we quantified N2O concentrations, environmental variables and the production pathways of N2O, measured the nitrogen isotope ratios of nitrate and ammonia to revealed the nitrogen pollution sources, assessed the isotopic ratios of N2O emitted from a series of polluted rivers and compare them with those of soils, oceans, and freshwaters, and revealed the influence of N2O production pathways and nitrogen pollution sources on the δ15N–N2O and N2O concentrations of urban polluted rivers in Shenzhen City, China. The concentrations of dissolved N2O ranged from 0.3 to 2482.9 nmol/L, with most values exceeding those equilibrium with the atmosphere, indicating that these rivers in urban subtropical areas are significant N2O sources to atmosphere. The isotopic ratios of dissolved N2O from polluted rivers varied widely, with δ15N–N2O ranging from −11.9‰ to 34.8‰, δ18O–N2O from 37.9‰ to 68.2‰, and SP from −10.5‰ to 36.2‰. The δ15N of emitted N2O from water surface to atmosphere ranged from −11.9‰ to +34.8‰, with a mean value of +9.2‰, which was higher than that from natural rivers, soil, and the troposphere. δ15Nsp and δ18O values of dissolved N2O were adopted to quantify the relative contributions of nitrification (f), denitrification (1-f), and the magnitude of N2O reduction (Fr) by denitrification. The results showed that denitrification was dominant pathway of N2O production, although the relative contribution of denitrification and nitrification had a great temporal and spatial variability. There is no distinct linear relationship between the concentrations of dissolved N2O, δ15N–N2O and environmental variables (DO, DOC, NO3−, and NH4+). The non-linear relationship among δ15N–N2O and δ15N–NO3−, f, Fr, and environmental variables were explored by regression tree analysis. The results suggested that f and Fr, not DO, DOC, NO3− and NH4+, were the primary correlates of dissolved N2O, for which the N2O concentrations were higher when N2O was primarily produced via nitrification (f > 77.5%) or denitrification (f < 8%), and were lower when Fr > 69.5%. It is the first attempt to reveal the connection between production and consumption processes with N2O concentrations directly. In addition, the elevated values of δ15N–NO3− (4.3 to 29.8‰) and δ15N–NH4+ (3.2‰ to 9.3‰) in these urban rivers consequence that the nitrogen contamination is predominantly sourced from urban sewage. Regression tree analysis also indicated that intense denitrification and sewage effluent result in enriched δ15N in N2O from polluted rivers, for which the δ15N values were higher when N2O was primarily produced via denitrification (f < 12%) or δ15N–NO3− were higher than 15.6‰. These findings provide a foundation upon which to devise strategies to reducing N2O production and emission in urban rivers.

Impact of influent strengths on nitrous oxide emission and its molecular mechanism in constructed wetlands treating swine wastewater

Constructed wetlands (CWs) can remove nitrogen (N) through plant assimilation and microbial nitrification and denitrification, while it also releases large greenhouse gas nitrous oxide (N2O) into the atmosphere. However, N2O emissions and the underlying microbial mechanisms of CWs when treating high-strength wastewater have not been systematically surveyed. Here, the effect of three influent strengths on N2O emissions in a pilot-scale CW treatment of swine wastewater was determined and the underlying microbial mechanisms were explored. The results showed that the removal rates of ammonium (NH4+) and total nitrogen (TN) increased significantly with the increasing influent strengths, however, the ratio of N2O emission/TN removal rose by 1.5 times at the same time. Quantitation of microorganisms responsible for N-cycle in the sediment indicated that the abundance of ammonia-oxidizing bacteria (AOB) in high influent strengths (COD, 962.38 ± 3.05 mg/L; NH4+, 317.89 ± 4.24 mg/L) was 51.6-fold compared with that in low influent strengths (COD, 516.94 ± 4.18 mg/L; NH4+, 100.65 ± 2.65), and AOB gradually replaced ammonia-oxidizing archaea (AOA) to dominate ammonia oxidizers. Structural equation models demonstrated that NO2− accumulations promoted the ratio of AOB/AOA, which further led to an increase in the ratio of N2O emission/TN removal. It is worth noting both the N removal rates and N2O emissions increased with the increasing influent strength. To obtain reduced N2O emissions, pretreatment technology for strength reduction should be supplemented before high-strength wastewater enters the CWs. This study may shed new light on the sustainable operation and application of CWs.

Organic Fertilization of Growing Media: Response of N Mineralization to Temperature and Moisture

Managing plant fertilization is a major concern of greenhouse growers when it comes to sustainable production on growing media. Organic fertilization is popular, but more difficult to control since organic compounds first need to be mineralized by microbes. The objective of this study was to characterize the time course of N mineralization by different fertilizer–growing media pairs, in the absence of plants. Several incubations were carried out at four temperatures (4, 20, 28, and 40 °C) and three suction potentials (−3.2, −10, and −31.6 kPa) on four growing media under two organic fertilization conditions to study the dynamics of NH4+ and NO3− production. The results showed that the release of mineral N was strongly dependent on growing media, temperature, humidity, and fertilizer nature, varying from 10.7% to 71.3% of the N fertilizer applied. A temperature action law was established for the four growing media. The Q10 value of the growing media was 1.13, lower than the average Q10 value of arable soils. On the other hand, the specific behavior of the growing media did not yield a single humidity action law. Nevertheless, the nitrification process, evaluated by analyzing the ratio of NO3− to total mineral N, showed a humidity-dependent relationship common to the four growing media and comparable to admitted observations on soils. Nitrification was optimal when growing media humidity was higher than 0.46 v/v.

Spatial distribution of the relationship between nitrate residues in soil and surface water quality revealed through attenuation factors

Thanks to the intense efforts over the past decades to reduce nutrient losses, the annual average nitrate (NO3-) concentrations in the European surface waters have decreased between 1990 and 2010, but the reduction has levelled off since then. Nitrogen (N) mitigation measures adapted to the local conditions are needed to further reduce the N pressure from agriculture on surface water quality. The NO3--N residue measured before the onset of winter has been used as a simple indicator of the N pressure from agriculture. However, the vulnerability of a stream to NO3- inputs depends on dilution and reduction of NO3- during its transport towards the surface water, which can be expressed by the attenuation factor for surface water (AFsw), i.e. the ratio of the average NO3- concentration at the bottom of the rooting zone and the average NO3- concentration in the surface water. In this study, we combined NO3--N measurements in the soil in autumn, NO3- concentrations measured in the surface water during the winter period and a relatively simple soil-crop model to calculate AFsw at subcatchment level, in order to estimate the effect of mitigation measures without collecting detailed information on the subsoil and groundwater processes. Simulations demonstrated that in Flanders (the northern part of Belgium) the further optimisation of the N fertilisation rate is the most effective measure to reduce surface water NO3- concentrations. Maximising the acreage of catch crops had a limited additional effect on the NO3- concentrations in surface water given that this is already widely practiced at present. Although the removal of N rich crop residues is highly effective at field level, it contributed little to the reduction of NO3- concentrations in the surface water because of the small acreage of these crops. The implemented scenarios show that in subcatchments with low AFSw, targeted and subcatchment-specific combinations of measures, but including the trade-off with the potential economic and other negative effects, may not be sufficient to obtain acceptable NO3- concentrations in the surface water at subcatchment level. In regions with low AFsw, end–of-pipe technologies might be more cost-effective and even imperative to avoid the risk of eutrophication and a low surface water quality.

PM2.5 and water-soluble inorganic ion concentrations decreased faster in urban than rural areas in China

We investigated variations of PM2.5 and water-soluble inorganic ions chemical characteristics at nine urban and rural sites in China using ground-based observations. From 2015 to 2019, mean PM2.5 concentration across all sites decreased by 41.9 µg/m3 with a decline of 46% at urban sites and 28% at rural sites, where secondary inorganic aerosol (SIAs) contributed to 21% (urban sites) and 17% (rural sites) of the decreased PM2.5. SIAs concentrations underwent a decline at urban locations, while sulfate (SO42–), nitrate (NO3–), and ammonium (NH4+) decreased by 49.5%, 31.3% and 31.6%, respectively. However, only SO42– decreased at rural sites, NO3– increased by 21% and NH4+ decreased slightly. Those changes contributed to an overall SIAs increase in 2019. Higher molar ratios of NO3– to SO42– and NH4+ to SO42– were observed at urban sites than rural sites, being highest in the heavily polluted days. Mean molar ratios of NH3/NHx were higher in 2019 than 2015 at both urban and rural sites, implying increasing NHx remained as free NH3. Our observations indicated a slower transition from sulfate-driven to nitrate-driven aerosol pollution and less efficient control of NOx than SO2 related aerosol formation in rural regions than urban regions. Moreover, the common factor at urban and rural sites appears to be a combination of lower SO42– levels and an increasing fraction of NO3– to PM2.5 under NH4+-rich conditions. Our findings imply that synchronous reduction in NOx and NH3 emissions especially rural areas would be effective to mitigate NO3–-driven aerosol pollution.

Competing pathways of cresol formation in toluene photooxidation: OH-toluene adducts react with NO2 or with O2?

Methyl-hydroxy-cyclohexadienyl radicals (OTAs) are the key products of the photooxidation of toluene, with implications for the fate of toluene. Hence, we investigated the photooxidation mechanisms and kinetics of three main OTAs (o-OTA, m-OTA, and p-OTA) with NO2 using quantum chemical calculations as well as the fate of OTAs under the different concentration ratios of NO2 and O2. The mechanism results show that the pathway of H-abstraction by NO2 to anti-HONO (anti-H-abstraction) is more favorable than the syn-H-abstraction pathway, because the strong interaction between OTAs and NO2 is formed in the transition states of the anti-H-abstraction pathways. The branching ratios of the anti-H-abstraction pathways are more than 99% in the temperature range of 216−298 K. The total rate constant of the OTA-NO2 reaction is 9.9 × 10−12 cm3/(molecule∙sec) at 298 K, which is contributed about 90% by o-OTA + NO2, and the main products are o-cresol and anti-HONO. The half-lives of the OTA-NO2 reaction in some polluted areas of China are 35 times longer than those of the OTA-O2 reaction. In the atmosphere, the NO2- and O2- initiated reactions of OTAs have the same ability to form cresols as [NO2] is up to 142.1 ppmV, which is impossible to achieve. It implies that under the experimental condition, the [NO2]/[O2] should be controlled to be less than 7.8 × 10−5 to simulate real atmospheric oxidation of toluene. Our results reveal that for the photooxidation of toluene, the yield of cresol is not affected by the concentration of NO2 under the atmospheric environment.

Variations in Sources, Composition, and Exposure Risks of PM2.5 in both Pre-Heating and Heating Seasons

“Clean Heating” (CH) was promoted in 2017 in north China. Nevertheless, CH impacts on PM2.5 chemical components, sources, and health risks in small cities remain unclear. A field measurement was taken at an urban site within the central Beijing-Tianjin-Hebei (BTH) region covering the pre-heating season (PHS) and heating season (HS) in the winter of 2019. PM2.5 concentrations (in µg m–3) increased from 69.1 in the PHS to 129 in the HS, reflecting the impacts of heating activities. Water-soluble ions dominated in terms of PM2.5, accounting for 32.0% in the PHS and 42.3% in the HS, respectively. On average, SO42– and NO3– (in µg m–3) were found to be markedly enhanced from 3.54 and 11.1 in the PHS to 13.1 and 23.2 in the HS, especially in the case of SO42–, reflecting the increased usage of coal/natural gas. Meanwhile, the ratios of NO3–/SO42– dropped from 2.75 in the PHS to 2.08 in the HS, implying drastic SO42– emissions from coal combustion used for heating. This may have been associated with the re-burning of coal for heating despite the “coal banning” law. Total carcinogenic risks (CRs) posed by inhalation of heavy metals increased from 6.61 × 10–6 in children and 2.64 × 10–5 in adults in the PHS to 8.23 × 10–6 and 3.29 × 10–5 in the HS. In contrast, the non-CRs for children and adults decreased in the HS due to a reduction in Ba of 85.5% in the HS. A total of seven sources, including fugitive dust (FD), vehicle exhaust (VE), coal combustion (CC), secondary inorganic aerosol (SIA), industrial emissions (IE), glass production (GP), and biomass burning (BB), were identified using a PMF model. The GP fraction decreased from 29.6% in the PHS to 2.59% in the HS due to strict emission control, which concurred with the decrease in Ba. The CC contribution increased significantly from 2.42% to 16.9%, indicating the CC was still serious in HS. Furthermore, the elevated BB share in the HS suggested that biomass was still being used as heating fuel.

A pathway for ZnO p-type transformation and its performance in solar cells

Aiming at the breakthrough of ZnO in solar cells, we investigate the theoretical rationality and experimental operability of its structural components. In this paper, First Principle Calculation is implemented to achieve the optimum doping ratio for ZnO p-type transformation. Then, Al-N co-doped ZnO films are prepared by magnetron sputtering. The quality of p-type ZnO films are controlled by changing the ratio of N2O to Ar in the sputtering atmosphere. Results shown that the p-type ZnO films with excellent photoelectrical properties can be successfully obtained in the condition of N2O:Ar = 1: 4, where the resistivity is as low asρ=3.678×10-5Ω·cm, the carrier concentration isN=1.3066×1021cm-3, the average transmittance of the visible region is about 90%. In addition, we first explore the feasibility on the fabrication of p-type Al-N co-doped ZnO/n-type Al-doped ZnO homojunction and its application in solar cell.

Influence of sample volume on nitrate N and O isotope ratio analyses with the denitrifier method.

Analyses of the isotope ratios of nitrogen (15 N/14 N) and oxygen (18 O/16 O) in nitrate (NO3 - ) with the denitrifier method require relatively high sample volumes at low concentrations (≤1 μM) to afford sufficient analyte for mass spectrometry, resulting in isotopic offsets compared to more concentrated samples of the same isotopic composition. To uncover the origins of isotopic offsets, we analyzed the N and O isotope ratios of NO3 - reference materials spanning concentrations of 0.5-20 μM. We substantiated the incidence of volume-dependent isotopic offsets, then investigated whether they resulted from (a) incomplete sample recovery during N2 O sparging, (b) blanks - bacterial, atmospheric, or in reference material solutions - and (c) oxygen atom exchange with water during the bacterial conversion of NO3 - to N2 O. Larger sample volumes resulted in modest offsets in δ15 N, but substantial offsets in δ18 O. N2 O recovery from sparging was less complete at higher volumes, resulting in decreases in δ15 N and δ18 O due to associated isotope fractionation. Blanks increased detectably with volume, whereas oxygen atom exchange with water remained constant within batch analyses, being sensitive to neither sample volume nor salinity. The sizeable offsets in δ18 O with volume are only partially explained by the factors considered in our analysis. Our observations argue for bracketing of NO3 - samples with reference materials that emulate sample volumes (concentrations) to achieve improved measurement accuracy and foster inter-comparability.

Temporal variations in the chemical composition of aerosols over the coastal Bay of Bengal

Variations in source, ionic composition and carbonaceous components of aerosols are expected in the atmosphere due to reversing the direction of winds from winter to summer over the coastal Bay of Bengal (BoB). To examine this monthly, samples were collected at the weekly interval between March 2016 and February 2017 in the coastal BoB. The air mass back trajectories suggested that the study region received aerosols from Indo-Gangetic Plain from October to February whereas from central India during June to September and south or southwest during March to May. A higher concentration of total suspended particulate matter (TSP) was observed from November to February (winter) compared to other months. The concentration of sulphate contributed more than half of water-soluble inorganic species followed by sodium, ammonium and nitrate. The dominant contribution of anthropogenic SO42− (>90%) to total SO42− was observed. The ambient elemental carbon loadings and organic carbon to EC ratios indicate the dominant contribution of biomass burning emissions in the study region. The significant contribution of non-sea salt sulphate and nss-K+ indicates a dominant contribution from the continental sources throughout the year. The mass ratio of NO3−/anthropogenic SO42− suggests stationary sources (i.e., coal burning in power plants) contribute significantly over vehicular emissions during the entire study period. The mass balance of ionic composition suggests the acidic nature of aerosols. The estimated secondary aerosols accounted for ∼50% of organic carbon and 7% of TSP in the study region. This study has implications for understanding the source, composition and nature of aerosols and possible impacts on coastal water upon its deposition.