PM Nitrate Research Articles

Jasmonic Acid Effect on Cucumis sativus L. Growth Is Related to Inhibition of Plasma Membrane Proton Pump and the Uptake and Assimilation of Nitrates.

When plants are exposed to environmental stress, their growth is inhibited. Under such conditions, controlled inhibition of growth is beneficial for plant survival. Jasmonic acid (JA) is a well-known phytohormone that limits plant growth, which has been confirmed in several species. However, its role in cucumber seedlings has not yet been comprehensively investigated. For this reason, we aimed to determine the involvement of JA in the regulation of proteins crucial for growth including plasma membrane proton pump (PM H+-ATPase), PM nitrate transporters, and nitrate reductase (NR). Treatment of cucumber seedlings with JA not only limited their growth but also increased the H2O2 content in their roots. The main sources of ROS generated for signalling purposes are PM NADPH oxidase (RBOH) and superoxide dismutase (SOD). Exposure of seedlings to JA induced the expression of some CsRBOH and SOD encoding genes, suggesting that ROS signalling can be activated by JA. As a consequence of JA exposure, the activity of all analysed proteins was inhibited and the expression of their genes was modified. The results indicate that reduction of PM H+-ATPase activity and the related decrease in nitrate uptake and assimilation are responsible for the root growth retardation of JA-treated plants.

Secondary PM<sub>2.5</sub> decreases significantly less than NO<sub>2</sub> emission reductions during COVID lockdown in Germany

Abstract. This study estimates the influence of anthropogenic emission reductions on the concentration of particulate matter with a diameter smaller than 2.5 µm (PM2.5) during the 2020 lockdown period in German metropolitan areas. After accounting for meteorological effects, PM2.5 concentrations during the spring 2020 lockdown period were 5 % lower compared to the same time period in 2019. However, during the 2020 pre-lockdown period (winter), PM2.5 concentrations with meteorology accounted for were 19 % lower than in 2019. Meanwhile, NO2 concentrations with meteorology accounted for dropped by 23 % during the 2020 lockdown period compared to an only 9 % drop for the 2020 pre-lockdown period, both compared to 2019. SO2 and CO concentrations with meteorology accounted for show no significant changes during the 2020 lockdown period compared to 2019. GEOS-Chem (GC) simulations with a COVID-19 emission reduction scenario based on the observations (23 % reduction in anthropogenic NOx emission with unchanged anthropogenic volatile organic compounds (VOCs) and SO2) are consistent with the small reductions of PM2.5 during the lockdown and are used to identify the underlying drivers for this. Due to being in a NOx-saturated ozone production regime, GC OH radical and O3 concentrations increased (15 % and 9 %, respectively) during the lockdown compared to a business-as-usual (BAU, no lockdown) scenario. Ox (equal to NO2+O3) analysis implies that the increase in ozone at nighttime is solely due to reduced NO titration. The increased O3 results in increased NO3 radical concentrations, primarily during the night, despite the large reductions in NO2. Thus, the oxidative capacity of the atmosphere is increased in all three important oxidants, OH, O3, and NO3. PM nitrate formation from gas-phase nitric acid (HNO3) is decreased during the lockdown as the increased OH concentration cannot compensate for the strong reductions in NO2, resulting in decreased daytime HNO3 formation from the OH + NO2 reaction. However, nighttime formation of PM nitrate from N2O5 hydrolysis is relatively unchanged. This results from the fact that increased nighttime O3 results in significantly increased NO3, which roughly balances the effect of the strong NO2 reductions on N2O5 formation. Ultimately, the only small observed decrease in lockdown PM2.5 concentrations can be explained by the large contribution of nighttime PM nitrate formation, generally enhanced sulfate formation, and slightly decreased ammonium. This study also suggests that high PM2.5 episodes in early spring are linked to high atmospheric ammonia concentrations combined with favorable meteorological conditions of low temperature and low boundary layer height. Northwest Germany is a hot-spot of NH3 emissions, primarily emitted from livestock farming and intensive agricultural activities (fertilizer application), with high NH3 concentrations in the early spring and summer months. Based on our findings, we suggest that appropriate NOx and VOC emission controls are required to limit ozone, and that should also help reduce PM2.5. Regulation of NH3 emissions, primarily from agricultural sectors, could result in significant reductions in PM2.5 pollution.

Formation and Prevention of Secondary Nitrate in PM2.5 in Tianjin

To study the formation and approaches to controlling secondary nitrate in PM2.5, the ionic compositions of PM2.5, pH of aerosols, variations in NH3-NH4+ and HNO3-NO3- concentrations, and the joint NH3/HNO3 sensitivity regime map of ammonium nitrate were investigated based on high-resolution online monitoring data for an urban site in central Tianjin from 2018 to 2019. The results showed that the average concentration of PM2.5 was 58μg·m-3, and the main ionic compositions of PM2.5 were nitrate (NO3-), ammonium (NH4+), sulfate (SO42-), Cl-, and K+ with corresponding mass percentages of 18.4%, 11.6%, 10.3%, 3.3%, and 2.6%, respectively. Concentrations of PM2.5 and the main components were relatively high during the heating season and relatively low during the non-heating season. The aerosols were weakly acidity with an average pH of 5.21; pH was higher in spring and winter and lower in summer and autumn, and diurnal variations pH were lower in the morning (00:00-08:00) and slightly higher at other times. The concentrations of NH3(g) (gas NH3) and HNO3(g) (gas HNO3) were 16.7μg·m-3and 1.2μg·m-3, respectively. The concentrations of NH3(g) were relatively higher from April to September and lower from October to February of the following year. HNO3(g) concentrations did not show any clear monthly pattern. Except during the summer, NH3(g) concentrations were higher in the morning and evening, and HNO3(g) concentrations were higher during the day. No clear linear relationships were observed between the concentrations of NH3(g) and NH4+ nor the concentrations of HNO3(g) and NO3- at different pH levels. Higher concentrations of NO3- and NH4+ were observed in the morning and evening, while no linear relationships were observed between the pH and concentrations of NH3(g)-NH4+ and HNO3(g)-NO3-. The joint NH3/HNO3 sensitivity regime map showed that most of the points were located in the HNO3 sensitive region with some in the NH3 & HNO3 sensitive region. In spring, autumn, and winter, most of the points were located in the HNO3 sensitive region while in summer, a significant quantity of the points were located in the NH3 & HNO3 sensitive region. Therefore, the precursors of HNO3 (such as NOx) should be controlled in the spring, autumn, and winter, and attention should be given to the control of the precursors of HNO3 (NOx) and NH3 in the summer to effectively control nitrate and ammonium aerosols in PM2.5 in Tianjin.

Deposition Velocity of Sulfate and Nitrate in PM2.5 above a Forest in Suburban Tokyo Using Relaxed Eddy Accumulation

Deposition Velocity of Sulfate and Nitrate in PM_2.5 above a Forest in Suburban Tokyo Using Relaxed Eddy Accumulation

Differences of Dry Deposition between Sulfate and Nitrate in PM2.5 to a Forest in Suburban Tokyo by Vertical Profile Observations

Differences of Dry Deposition between Sulfate and Nitrate in PM_2.5 to a Forest in Suburban Tokyo by Vertical Profile Observations

Insights into factors affecting nitrate in PM2.5 in a polluted high NOx environment through hourly observations and size distribution measurements

AbstractNitrate, a major PM2.5 component in polluted environments, could be greatly elevated during pollution episodes. In this study, nitrate and other inorganic ions on PM2.5 were measured half hourly at a residential location in Hong Kong in December 2009. Hourly nitrate concentrations in PM2.5 varied from 0.8 to 40.5 µg m−3. In an episode during which hourly visibility was down to 3.7 ± 1.0 km and NO2 was 80.7 ± 14.4 ppb, PM2.5 NO3− reached 27.8 ± 8.0 µg m−3, ~6 times the level during the normal hours. Nitrate was fully balanced by NH4+, indicating abundant presence of NH3. Size‐segregated measurements showed 84% of nitrate was in the fine mode during the episode and also suggested that less acidic fine particles and less abundant sea‐salt particles were the contributing factors to the dominant presence in the fine mode. An observation‐based model for secondary inorganic aerosols was applied to investigate the relative importance of homogeneous and heterogeneous reactions to production of NO3− potential (sum of HNO3 (g) and aerosol nitrate). The modeling analysis shows that both formation pathways were significantly more active during the episode. Gas phase production of HNO3 through reaction of NO2 + OH dominated during the initial rapid buildup of nitrate around noon time, but the heterogeneous N2O5 hydrolysis pathway made a sizable contribution in the subsequent few hours due to sustained high‐NO2 concentrations combined with reduced photolysis loss of N2O5. This case study illustrates the important role of NH3 and NO2 in elevating PM2.5 in a high‐NOx environment through the formation of nitrate.

Overview of the LADCO winter nitrate study: hourly ammonia, nitric acid and PM<sub>2.5</sub> composition at an urban and rural site pair during PM<sub>2.5</sub> episodes in the US Great Lakes region

Abstract. An overview of the LADCO (Lake Michigan Air Directors Consortium) Winter Nitrate Study (WNS) is presented. Sampling was conducted at ground level at an urban-rural pair of sites during January–March 2009 in eastern Wisconsin, toward the western edge of the US Great Lakes region. Areas surrounding these sites experience multiday episodes of wintertime PM2.5 pollution characterized by high fractions of ammonium nitrate in PM, low wind speeds, and air mass stagnation. Hourly surface monitoring of inorganic gases and aerosols supplemented long-term 24-h aerosol chemistry monitoring at these locations. The urban site (Milwaukee, WI) experienced 13 PM2.5 episodes, defined as periods where the seven-hour moving average PM2.5 concentration exceeded 27 μg m−3 for at least four consecutive hours. The rural site experienced seven episodes by the same metric, and all rural episodes coincided with urban episodes. Episodes were characterized by low pressure systems, shallow/stable boundary layer, light winds, and increased temperature and relative humidity relative to climatological mean conditions. They often occurred in the presence of regional snow cover at temperatures near freezing, when snow melt and sublimation could generate fog and strengthen the boundary layer inversion. Substantial contribution to nitrate production from nighttime chemistry of ozone and NO2 to N2O5 and nitric acid is likely and requires further investigation. Pollutant-specific urban excess during episode and non-episode conditions is presented. The largest remaining uncertainties in the conceptual model of the wintertime episodes are the variability from episode-to-episode in ammonia emissions, the balance of daytime and nighttime nitrate production, the relationship between ammonia controls, NOx controls and ammonium nitrate reductions, and the extent to which snow and fog are causal (either through meteorological or chemical processes) rather than just correlated with episodes because of similar synoptic meteorology.

Evaluating PM2.5 ionic components and source apportionment in Jinan, China from 2004 to 2008 using trajectory statistical methods

The mass concentrations and major chemical components of PM(2.5) in Jinan, Shandong Province, China from Dec. 2004 to Oct. 2008 were analyzed using backward trajectory cluster analysis in conjunction with the potential source contribution function (PSCF) model. The aim of this work was to study the inter-annual variations of mass concentrations and major chemical components of PM(2.5), evaluate the air mass flow patterns and identify the potential local and regional source areas that contributed to secondary sulfate and nitrate in PM(2.5) in Jinan. The annual mean concentrations of PM(2.5), sulfate and nitrate in 2004-2008 were almost the highest in the world. The most significant air parcels contributing to the highest mean concentrations of mass and secondary ions in PM(2.5) originated from the industrialized areas of Shandong Province. Clusters with a lower ratio of NO(3)(-)/SO(4)(2-) in PM(2.5) originated from the Yellow Sea, while a higher ratio was observed in the clusters passing through Beijing and Tianjin. PSCF modeling indicated that the provinces of Shandong, Henan, Jiangsu, Anhui and the Yellow Sea were the major potential source regions for sulfate, in agreement with the cluster analysis results. Regional and long-range transport of NH(4)NO(3) played an important role in the nitrate concentration of Jinan. By comparing the distributions of secondary sulfate and nitrate over three years, enhanced emission control management before and during the 29(th) Olympic Games led to a discernible decrease in source contributions from Beijing and its environs in 2007-2008.

Temporal characteristics from continuous measurements of PM 2.5 and speciation at the Taipei Aerosol Supersite from 2002 to 2008

This study uses monitoring data collected at the Taipei Aerosol Supersite from March 2002 to February 2008 to analyze characteristics such as seasonal fluctuations, diurnal variations, and photochemical-related variations of PM 2.5 chemical compositions. The results indicate that the average of PM 2.5 mass concentration in Taipei during this period is 30.3 ± 16.0 μg m −3. The highest average concentration of PM 2.5 components is that of sulfate, which accounts for 21.1% of the PM 2.5 mass, followed by organic carbon (OC) at 15.9%, nitrate at 5.8%, and elemental carbon (EC) at 5.4%. Concentrations of EC, OC, and nitrate have distinctive but similar seasonal fluctuations, which is highest in spring and lowest in fall. Sulfate concentration has less seasonal fluctuations, and the highest value appears during the fall. Similarly, concentrations of EC, OC, and nitrate have notable diurnal variations; however, the diurnal variation of sulfate concentration is not very apparent. These observation data show that EC, OC, and nitrate in PM 2.5 in the Taipei metropolis come mainly from local emissions, while sulfate comes mainly from the regional transport of pollutants. This is likely because Taiwan is located on the lee zone of the Asian prevailing winds from fall to spring; its air quality is frequently affected by the transport of air pollutants from Mainland China. In addition, the extent of increase in aerosols is much higher than that of CO, indicating the formation of secondary aerosol when photochemical activity is strong. Based on six years of observation data, this study explores three potential scenarios to set up Taiwan's PM 2.5 air quality standard (AQS). The analysis indicates that the optimum standard for 24-h air quality of PM 2.5 should be around 50 μg m −3.

Modeling wintertime particulate matter formation in central California

A wintertime episode during the 2000 California Regional PM Air Quality Study (CRPAQS) was simulated with the air quality model CMAQ–MADRID. Model performance was evaluated with 24-h average measurements available from CRPAQS. Modeled organic matter (OM) was dominated by emissions, which were probably significantly under-represented, especially in urban areas. In one urban area, modeled daytime nitrate concentrations were low and evening concentrations were high. This diurnal profile was not explained by the partition of nitrate between the gas and particle phases, because gaseous nitric acid concentrations were low compared to PM nitrate. Both measured and simulated nitrate concentrations aloft were lower than at the surface at two tower locations during this episode. Heterogeneous reactions involving NO 3 and N 2O 5 accounted for significant nitrate production in the model, resulting in a nighttime peak. The sensitivity of PM nitrate to precursor emissions varied with time and space. Nitrate formation was on average sensitive to NO x emissions. However, for some periods at urban locations, reductions in NO x caused the contrary response of nitrate increases. Nitrate was only weakly sensitive to reductions in anthropogenic VOC emissions. Nitrate formation tended to be insensitive to the availability of ammonia at locations with high nitrate, although the spatial extent of the nitrate plume was reduced when ammonia was reduced. Reductions in PM emissions caused OM to decrease, but had no effect on nitrate despite the role of heterogeneous reactions. A control strategy that focuses on NO x and PM emissions would be effective on average, but reductions in VOC and NH 3 emissions would also be beneficial for certain times and locations.

Simulation of long-range transport aerosols from the Asian Continent to Taiwan by a Southward Asian high-pressure system

Aerosol is frequently transported by a southward high-pressure system from the Asian Continent to Taiwan and had been recorded a 100% increase in mass level compared to non-event days from 2002 to 2005. During this time period, PM 2.5 sulfate was found to increase as high as 155% on event days as compared to non-event days. In this study, Asian emission estimations, Taiwan Emission Database System (TEDS), and meteorological simulation results from the fifth-generation Mesoscale Model (MM5) were used as inputs for the Community Multiscale Air Quality (CMAQ) model to simulate a long-range transport of PM 2.5 event in a southward high-pressure system from the Asian Continent to Taiwan. The simulation on aerosol mass level and the associated aerosol components were found within a reasonable accuracy. During the transport process, the percentage of semi-volatile PM 2.5 organic carbon in PM 2.5 plume only slightly decreased from 22–24% in Shanghai to 21% near Taiwan. However, the percentage of PM 2.5 nitrate in PM 2.5 decreased from 16–25% to 1%. In contrast, the percentage of PM 2.5 sulfate in PM 2.5 increased from 16–19% to 35%. It is interesting to note that the percentage of PM 2.5 ammonium and PM 2.5 elemental carbon in PM 2.5 remained nearly constant. Simulation results revealed that transported pollutants dominate the air quality in Taipei when the southward high-pressure system moved to Taiwan. Such condition demonstrates the dynamic chemical transformation of pollutants during the transport process from continental origin over the sea area and to the downwind land.

Major factors affecting the ambient particulate nitrate level at Gosan, Korea

Major factors that determine the ambient particulate nitrate concentration at Gosan, Jeju Island, Korea are identified based on the inorganic ionic and elemental data in TSP and PM 2.5 measured between March 1998 and February 2003. It was found that the nitrate in TSP was highly correlated with crustal species such as nss-Ca 2+ and nss-Mg 2+, while nitrate in PM 2.5 was highly correlated with anthropogenic species such as NH 4 +. In the high nitrate cases in TSP, the concentrations of crustal species and NH 4 + were high and the air parcels moved mostly from Mongolia. In the high nitrate cases in PM 2.5, the concentration of NH 4 + was high and the air parcels moves mostly from southern China. It was found that the air parcels were mainly from the Pacific Ocean for the low nitrate cases. Still there was significant number of the low nitrate cases with air parcels from Mongolia for both TSP and PM 2.5. In these cases, the concentrations of crustal species were low for TSP and those of NH 4 + were low for PM 2.5. Therefore, the most important factors that determined the level of nitrate were the concentration of crustal species for TSP and the concentration of NH 4 + for PM 2.5 irrespective of air parcel movement.

Effects of Sulfur Dioxide and Oxides of Nitrogen Emission Reductions on Fine Particulate Matter Mass Concentrations: Regional Comparisons

Two thermodynamic equilibrium models were applied to estimate changes in mean airborne fine particle (PM2.5)mass concentrations that could result from changes in ambient concentrations of sulfate, nitric acid, or ammonia in the southeastern United States, the midwestern United States, and central California. Pronounced regional differences were found. Southeastern sites exhibited the lowest current mean concentrations of nitrate, and the smallest predicted responses of PM2.5 nitrate and mass concentrations to reductions of nitric acid, which is the principal reaction product of the oxidation of nitrogen dioxide (NO2) and the primary gas-phase precursor of fine particulate nitrate. Weak responses of PM2.5 nitrate and mass concentrations to changes in nitric acid levels occurred even if sulfate concentrations were half of current levels. The midwestern sites showed higher levels of fine particulate nitrate, characterized by cold-season maxima, and were projected to show decreases in overall PM levels following decreases of either sulfate or nitric acid. For some midwestern sites, predicted PM2.5 nitrate concentrations increased as modeled sulfate levels declined, but sulfate reductions always reduced the predicted fine PM mass concentrations; PM2.5 nitrate concentrations became more sensitive to reductions of nitric acid as modeled sulfate concentrations were decreased. The California sites currently have the highest mean concentrations of fine PM nitrate and the lowest mean concentrations of fine PM sulfate. Both the estimated PM2.5 nitrate and fine mass concentrations decreased in response to modeled reductions of nitric acid at all California sites. The results indicate important regional differences in expected PM2.5 mass concentration responses to changes in sulfate and nitrate precursors. Analyses of ambient data, such as described here, can be a key part of weight of evidence (WOE) demonstrations for PM2.5 attainment plans. Acquisition of the data may require special sampling efforts, especially for PM2.5 precursor concentration data.

MICS Asia Phase II—Sensitivity to the aerosol module

In the framework of the model intercomparison study—Asia Phase II (MICS2), where eight models are compared over East Asia, this paper studies the influence of different parameterizations used in the aerosol module on the aerosol concentrations of sulfate and nitrate in PM 10 . An intracomparison of aerosol concentrations is done for March 2001 using different configurations of the aerosol module of one of the model used for the intercomparison. Single modifications of a reference setup for model configurations are performed and compared to a reference case. These modifications concern the size distribution, i.e. the number of sections, and physical processes, i.e. coagulation, condensation/evaporation, cloud chemistry, heterogeneous reactions and sea-salt emissions. Comparing monthly averaged concentrations at different stations, the importance of each parameterization is first assessed. It is found that sulfate concentrations are little sensitive to sea-salt emissions and to whether condensation is computed dynamically or by assuming thermodynamic equilibrium. Nitrate concentrations are little sensitive to cloud chemistry. However, a very high sensitivity to heterogeneous reactions is observed. Thereafter, the variability of the aerosol concentrations to the use of different chemistry transport models (CTMs) and the variability to the use of different parameterizations in the aerosol module are compared. For sulfate, the variability to the use of different parameterizations in the aerosol module is lower than the variability to the use of different CTMs. However, for nitrate, for monthly averaged concentrations averaged over four stations, these two variabilities have the same order of magnitude.

Seasonal variation of ionic species in fine particles at Qingdao, China

Totally nine measurement campaigns for ambient particles and SO 2 have been conducted during the period of 1997–2000 in Qingdao in order to understand the characteristics of the particulate matter in coastal areas of China. The mass fractions of PM 2.5, PM 2.5−10 and PM >10 in TSP are 49%, 25% and 26%, respectively. The size distribution of particles mass concentrations in Qingdao shows bi-modal distribution. Mass fraction percentages of water-soluble ions in PM 2.5, PM 2.5−10 and PM >10 decreased from 62% to 35% and 21%. In fine particles, sulfate, nitrate and ammonium, secondary formed compounds, are major components, totally accounting for 50% of PM 2.5 mass concentration. The ratios of sulfate, chloride, ammonium and potassium in PM 2.5 for heating versus non-heating periods are 1.34, 1.80, 1.56 and 1.44, respectively. The ratio of nitrate is 3.02 and this high ratio could be caused by reduced volatilization at lower temperature. Sulfate concentrations are higher than nitrate in PM 2.5. The chemical forms of sulfate and nitrate are probably (NH 4) 2SO 4 and NH 4NO 3 and chloride depletion was observed. Backward trajectory analysis reflected possible influence of air pollutant transport to Qingdao local aerosol pollution.