Particulate Nitrate Research Articles

A Satellite-Based Indicator for Diagnosing Particulate Nitrate Sensitivity to Precursor Emissions: Application to East Asia, Europe, and North America.

Particulate nitrate is a major component of fine particulate matter (PM2.5) and a key target for improving air quality. Its formation is varyingly sensitive to emissions of nitrogen oxides (NOx ≡ NO + NO2), ammonia (NH3), and volatile organic compounds (VOCs). Diagnosing the dominant sensitivity is critical for effective pollution control. Here, we show that satellite observations of the NO2 column and the NH3/NO2 column ratio can effectively diagnose the dominant sensitivity regimes in polluted regions of East Asia, Europe, and North America, in different seasons, though with reduced performance in the summer. We demarcate the different sensitivity regimes using the GEOS-Chem chemical transport model and apply the method to satellite observations from the OMI (NO2) and IASI (NH3) in 2017. We find that the dominant sensitivity regimes vary across regions and remain largely consistent across seasons. Sensitivity to NH3 emissions dominates in the northern North China Plain (NCP), the Yangtze River Delta, South Korea, most of Europe, Los Angeles, and the eastern United States. Sensitivity to NOx emissions dominates in central China, the Po Valley in Italy, the central United States, and the Central Valley in California. Sensitivity to VOCs emissions dominates only in the southern NCP in the winter. These results agree well with those of previous local studies. Our satellite-based indicator provides a simple tool for air quality managers to choose emission control strategies for decreasing PM2.5 nitrate pollution.

Combined-phase source apportionment of ambient PM2.5, PAHs and VOCs from an industrialized environment: Consequences of photochemical initial concentrations.

Air pollutants in the particulate (PM2.5 species, PAHs) and gaseous phases (VOCs) collected between 2013 and 2019 once every three or six days for a period of 24 hours in an industrialized city in Ontario were analyzed to apportion their common sources. The consequences of using these species jointly for receptor modelling were assessed via combined-phase source apportionment that used the data as is, and in a protocol that factored in the potential for photochemical losses of gas-phase species. Thus, photochemically corrected initial concentrations (PIC) were calculated. Analyses of the inputs followed either with positive matrix factorization or its dispersion-normalized variant (DN-PMF). Comparisons of applying PMF to the originally observed input data (BASE) and DN-PMF on data with PIC corrections were made. When the inputs consisted only of VOCs, three factors were resolved with BASE PMF: natural gas, vehicular emissions, and industrial emissions co-emitted with summertime gasoline evaporation. A fourth factor was obtained, representing reactive VOCs when DN-PIC PMF was used. When the combined phase input data were analyzed, nine factors were resolved for both BASE and DN-PIC PMF. These factors in order of diminishing average PM mass contributions were: particulate sulphate, secondary organic aerosol (SOA), particulate nitrate (pNO3), biomass burning with natural gas, crustal matter, winter blend of gasoline, coking/coal combustion, steelmaking, and summer blend/light duty vehicular emissions. When BASE and DN-PIC PMF results are compared, the average PM mass contribution of the summer gasoline fuel factor increased from 2% in BASE case to 5%, suggesting severe underestimation of this source’s contributions without DN-PIC. Also, substantial increases of reactive VOCs in the SOA factor, and PAHs with ≥four rings in the pNO3 and steelmaking factors were observed with DN-PIC PMF compared to the BASE PMF case, indicating that for SOA, reactive VOCs at this location contributed to SOA sources.

The response of daytime nitrate formation to source emissions reduction based on chemical kinetic and thermodynamic model

Particulate nitrate is an important component of particulate matter and poses a significant threat to the ecosystem and human health. The gas-phase formation pathway of nitrate is extremely important, which mainly comprises the NO2 oxidation process triggered by OH radicals and the nitrate partitioning process. The response of nitrate to source emission reduction during different pollution periods remains unclear. Here, we applied the chemical kinetic and thermodynamics model to explore the importance oxidation process and partitioning process during different pollution periods based on high-time resolution observation data. The result indicated that with the aggravation of pollution, the partitioning process gradually ceases to be a limiting step in the formation of nitrates. The results of the influencing factor analysis indicate that NO2 concentration and aerosol pH values play a more significant role in the formation of nitrates. Specifically, during the clean period, nitrate formation is sensitive to both NO2 concentration and pH values, but during the pollution period, it becomes sensitive only to NO2 concentration. By combining source apportionment, we explored the response of nitrate formation to source emission reduction, and the results showed that the control of vehicle exhaust emissions and coal combustion sources is more effective in mitigating nitrate pollution. Additionally, this study also emphasized the importance of early prevention and control of pollution sources. This research provides scientific evidence for the precise management and control of nitrates.

Effects of Ammonia Mitigation on Secondary Organic Aerosol and Ammonium Nitrate Particle Formation in Photochemical Reacted Gasoline Vehicle Exhausts

Gaseous air pollutants emitted primarily by anthropogenic sources form secondary products through photochemical reactions, complicating the regulatory analysis of anthropogenic emissions in the atmosphere. We used an environmental chassis dynamometer and a photochemical smog chamber to conduct a parameter sensitivity experiment to investigate the formation of secondary products from a gasoline passenger car. To simulate the mitigation of ammonia emissions from gasoline vehicle exhausts assuming future emission controls and to allow photochemical oxidation and aging of the vehicle exhaust, ammonia was selectively removed by a series of five denuders installed between the vehicle and photochemical smog chamber. Overall, there were no differences in the formation of secondary organic aerosols and ozone with or without ammonia mitigation. However, the potential for ammonium nitrate particle formation was significantly reduced with ammonia mitigation. In addition, ammonia mitigation resulted in increased aerosol acidity due to nitric acid in the gas phase not being neutralized by ammonia and condensing onto the liquid particle phase, indicating a potentially important secondary effect associated with ammonia mitigation. Thus, we provide new insights into the effects of ammonia mitigation on secondary emissions from gasoline vehicle exhaust and into a potentially useful experimental approach for determining primary and secondary emissions.

Hygroscopic growth and activation changed submicron aerosol composition and properties in the North China Plain

Abstract. Aerosol hygroscopic growth and activation under high-relative-humidity (RH) conditions significantly influence the physicochemical properties of submicron aerosols (PM1). However, this process remains poorly characterized due to limited measurements. To address this gap, we deployed an advanced aerosol–fog sampling system that automatically switched between PM1, PM2.5 and total suspended particulate (TSP) inlets at a rural site in the North China Plain in the cold season. The results revealed that aerosol swelling due to water vapor uptake influenced aerosol sampling under high-RH conditions by shifting the cut-off size of impactors. At subsaturated high RH (> 90 %), over 25 % of aerosol mass with dry diameters below 1 µm resided in supermicron ranges, while in supersaturated foggy conditions, more than 70 % of submicron aerosol migrated to supermicron ranges. Hygroscopic growth and activation particularly affected highly hydrophilic inorganic salts, shifting a significant number of submicron sulfate and nitrate particles to supermicron ranges, with 27 %–33 % at 95 % ≤ RH ≤ 99 % and more than 78 % under supersaturated foggy conditions. Moreover, more than 10 % of submicron biomass burning organic aerosols grew beyond 2.5 µm during fog events, while fossil-fuel-related organic aerosol (FFOA) remained dominantly in submicron ranges, suggesting inefficient aqueous conversion of FFOA. The two secondary organic aerosol (SOA) factors (OOA1 and OOA2) behaved differently under supersaturated conditions, with OOA2 exhibiting a higher activated fraction despite a lower oxygen / carbon ratio. A substantial increase in organic nitrate and organosulfur mass concentrations in activated droplets during fog events suggested aqueous conversions and formations of brown carbon with potential radiative impacts. Overall, our study highlights remarkably different cloud and fog processing behaviors between primary and secondary aerosols, which would benefit a better understanding of aerosol–cloud interactions under distinct atmospheric conditions.

Strong upwards transport of HONO in daytime over urban area of Beijing, China

Strong upwards transport of Nitrous acid (HONO) in daytime over urban area of Beijing was observed based on combined observations of HONO, NOx (NO and NO2), nitrate, and PM2.5 at two heights (90 m and 528 m) on the highest building of Beijing (528 m above ground). The mean HONO at the 528 m (0.26 ppb) was lower than that at the 90 m (0.54 ppb), and a clear difference in diurnal variation of HONO between the two heights was observed. HONO at the 90 m showed two peaks in the morning rush hour and mid-night, but decreased sharply in daytime (e.g., from 0.62 ppb at 08:00 to 0.34 at 14:00); while the decreasing trend of HONO in daytime significantly weakened at the 528 m (e.g., from 0.26 ppb at 08:00 to 0.27 at 14:00).With PBL development in the morning, HONO in low layer was upwards transported to the 528 m, which compensated partly HONO loss via photolysis and resulted in a relatively stable concentration at the 528 m in daytime. A positive relationship of the bulk Richardson number (Ri) in 0–500 m with the difference of HONO between the two heights during daytime (08:00–18:00) confirmed the above analyses. HONO budget analysis indicated that a strong unknown HONO source existed at the 528 m in daytime, which was negative correlated to the Ri. These results further confirmed that vertical transport of HONO from low layer was a potential HONO source at the 528 m. Moreover, the contribution of photolysis of particulate nitrate significantly increased at the 528 m. Its contribution in total HONO sources increased from 11.9 % at the 90 m to 16.0 % at the 528 m.

Atmospheric reactive nitrogen conversion kicks off the co-directional and contra-directional effects on PM2.5-O3 pollution

As the two important ambient air pollutants, particulate matter (PM2.5) and ozone (O3) can both originate from gas nitrogen oxides. In this study, applied by theoretical analysis and machine learning method, we examined the effects of atmospheric reactive nitrogen on PM2.5-O3 pollution, in which nitric oxide (NO), nitrogen dioxide (NO2), gaseous nitric acid (HNO3) and particle nitrate (pNO3−) conversion process has the co-directional and contra-directional effects on PM2.5-O3 pollution. Of which, HNO3 and SO2 are the co-directional driving factors resulting in PM2.5 and O3 growing or decreasing simultaneously; while NO, NO2, and temperature represent the contra-directional factors, which can promote the growth of one pollutant and reduce another one. Our findings suggest that designing the suitable co-controlling strategies for PM2.5-O3 sustainable reduction should target at driving factors by considering the contra-directional and co-directional effects under suitable sensitivity regions. For co-directional driving factors, the design of suitable mitigation strategies will jointly achieve effective reduction in PM2.5 and O3; while for contra-directional driving factors, it should be more patient, otherwise, it is possible to reduce one item but increase another one at the same time.

Quantifying HONO Production from Nitrate Photolysis in a Polluted Atmosphere.

The photolysis of particulate nitrate (pNO3-) has been suggested to be an important source of nitrous acid (HONO) in the troposphere. However, determining the photolysis rate constant of pNO3- (jpNO3-) suffers from high uncertainty. Prior laboratory measurements of jpNO3- using aerosol filters have been complicated by the "shadow effect"─a phenomenon of light extinction within aerosol layers that potentially skews these measurements. We developed a method to correct the shadow effect on the photolysis rate constant of pNO3- for HONO production (jpNO3-→HONO) using aerosol filters with identical chemical compositions but different aerosol loadings. We applied the method to quantify jpNO3-→HONO over the North China Plain (NCP) during the winter haze period. After correcting for the shadow effect, the normalized average jpNO3-→HONO at 5 °C increased from 5.89 × 10-6 s-1 to 1.72 × 10-5 s-1. The jpNO3-→HONO decreased with increasing pH and nitrate proportions in PM2.5 and had no correlation with nitrate concentrations. A parametrization for jpNO3-→HONO was developed for model simulation of HONO production in NCP and similar environments.

An analysis of the PM10 chemical composition and its spatial and seasonal variation in Piedmont (Italy) using Raman spectroscopy

Particulate Matter (PM) dramatically affects the well-being of a growing global population, particularly in urban areas. While air quality control is an important and pressing issue, particulate matter analysis typically focuses on size distribution and concentration, offering limited insights into chemical composition and pollutant sources.This study analyzes PM10 samples collected from five air quality monitoring stations across the Piedmont region. Specifically, the two of the stations are located in the urban environment of Turin, a city known as one of Europe's most polluted cities. The analysis has been carried out using primarily Raman Spectroscopy (RS) to identify the main PM components, investigate the different PM compositions, and evaluate the chemical and seasonal variations. Scanning Electron Microscopy (SEM) equipped with an Energy Dispersion X-ray spectrophotometer (EDX) has also been used to obtain further information about the elemental composition and the size distribution.Amorphous carbon, nitrate salt, sulfate salt, iron oxides, and quartz are the main compounds found. The results of our study highlight significant differences in the chemical composition of PM10, indicating variations in the sources and characteristics of PM. Notably, higher levels of nitrate and sulfate particles are linked respectively to cold and warm seasons. Whereas, amorphous carbon and iron oxides are associated with distinct geographic features at the sampling sites, such as traffic conditions. These findings emphasize the importance of understanding the different sources and characteristics of PM10 to develop effective air pollution mitigation strategies in the Piedmont region.

Enhanced formation of nitrogenous organic aerosols and brown carbon after aging in the planetary boundary layer

Particulate organic nitrates (pON) significantly contribute to the mass of organic aerosol and influence the nitrogen oxides cycle in the atmosphere, but their evolution and lifetime remain uncertain. This study performed simultaneous measurements on the anthropogenically affected surface site and the mountain site on top of the polluted planetary boundary layer (PBL). After aging in the PBL, organic nitrate was converted from primary sources (decreased from 8.7% to 4.3%) to secondary sources (increased from 6.3% to 36.1%), spanning from the surface to the mountain. The evaporation of more volatile inorganic nitrate and the production of secondary organic nitrate during aging in the PBL contributed to the enhanced pON fraction over the top of PBL. The contribution of light absorption by brown carbon increased by 57% at the top of PBL compared to the surface, consistent with the higher fraction of nitrogenous organic aerosols over the mountain. The results provide field evidence that the nitrogenous organic aerosols (OA) may be preserved by adding into secondary OA and significantly contribute to the enhanced importance of brown carbon after aging during vertical transport in the PBL.

Machine learning exploring the chemical compositions characteristics and sources of PM2.5 from reduced on-road activity

Particulate nitrate pollution has emerged as a major contributor to haze events in urban environment, due to the rapid increase of vehicle emissions. However, a comprehensive formation mechanisms of PM2.5 responses to vehicle emissions control still remains high uncertainties. In our study, hourly criteria air pollutants, meteorological parameters and chemical compositions of PM2.5 were continuously measured with or without reduced on-road activity at the coastal city in southeast China. XG Boost-SHAP models analysis showed that increasing concentrations of NO3−, NH4+, and BC contribute to elevated PM2.5 levels, due to the influence of vehicle emissions. Based on PMF model results, there was a notable increase in the contributions of traffic-related emissions, industrial activities, and dust sources to PM2.5, with increments of 13%, 4%, and 7%, respectively. In addition, metal elements such as Mn emerged as the primary contributor to hazard quotient (HQ) values, originated from non-exhaust emissions of vehicles, which might cause the potential toxic risks on human health, particularly during haze events. Hence, this study improve the understanding of air quality and human health both direct and indirect responses to vehicle emissions control in future urban management.

Secondary Organic Aerosol Formation from Aqueous Ethylamine Oxidation Mediated by Particulate Nitrate Photolysis

Secondary Organic Aerosol Formation from Aqueous Ethylamine Oxidation Mediated by Particulate Nitrate Photolysis

The challenge of cellulose nitrate-coated fabrics: molecular characterization of celluloid detachable collars and Fabrikoid

In the 19th century, significant linen and leather imitation products were invented using cellulose nitrate-coated fabrics, including celluloid detachable collars and Fabrikoid artificial leather, now preserved in the Hagley Museum and Library, USA. Using optical microscopy, µRaman, and µFourier Transformed Infrared spectroscopies, this study highlights the need for characterizing the heterogeneity of these materials at the microscale. While the detachable collars have well-preserved fabric coatings composed of cellulose nitrate, camphor, anatase (TiO2), and carbon-based particles, Fabrikoid’s pigmented cellulose nitrate-castor oil systems show problems. Our molecular data align with a 1922 report on Fabrikoid degradation, revealing free fatty acids and carboxylates formed due to oil oxidation. This is concerning as these materials were used until the 1960s, demonstrated by the analysis of objects from the National Museum of Costumes in Portugal. Future studies should address the compatibility of cellulose nitrate with fatty acids and the reactivity of additives in these systems.

Precise counter anion modulation of the self-assembly behavior-endowed ultrasensitive and specific dual-mode visualization of nitrate

Pt(II) polypyridine complex-based probe exhibits promising performance in anion detection by the change of the absorption and emission properties based on supramolecular self-assembly. However, whether one can develop a modulation strategy of the counter anion to boost the detection sensitivity and anti-interference capability of the Pt(II) complex-based probe remains a big challenge. Here, an effective modulation strategy was proposed by precisely regulating the interaction energy through adjusting the type of the counter anions, and a series of probes have been synthesized by counter anion (X = Cl-, ClO4-, PF6-) exchange in [Pt(tpy)Cl]·X (tpy=2,2′:6′,2′’-terpyridine), and thus the colorimetric-luminescence dual-mode detection toward nitrate was achieved. The optimal [Pt(tpy)Cl]·Cl probe shows superior nitrate detection performance including a limit of detection (LOD) (8.68 nM), rapid response (<0.5 s), an excellent selectivity and anti-interference capability even facing 14 common anions. Moreover, a polyvinyl alcohol (PVA) sponge-based sensing chip loaded with the probe enables the ultra-sensitive detection of nitrate particles with an ultralow detection limit of 7.6 pg, and it was further integrated into a detection pen for the accurate recognition of nitrate particles in real scenarios. The proposed counter-anion modulation strategy is expected to start a new frontier for the exploration of novel Pt(II) complex-based probes.

Sources and formation characteristics of particulate nitrate in the Pearl River Delta region of China: Insights from three-year online observations

Nitrate (NO3−) has been identified as a key component of particulate matter (PM2.5) in China. However, there is still a lack of understanding regarding its sources and how it forms, especially in the context of high-frequency and long-term data. In this study, NO3− levels were observed on an hourly basis over an almost three-year period at an urban site in the Pearl River Delta (PRD) region, China, from January 2019 to December 2021. The results reveal an average daily NO3− concentration ranging from 0.08 μg m−3 to 61.69 μg m−3, constituting 11.9 ± 12.5 % of PM2.5. This percentage rose to as high as 57 % during pollution episodes, highlighting NO3−'s significant role in pollution formation. The ammonia-rich environment was found to be the most important factor in promoting NO3− formation. Positive Matrix Factorization (PMF) analysis indicates that the primary sources of NO3− in the PRD region were vehicle emissions (43.8 ± 21.2 %) and coal combustion (39.1 ± 21.5 %), with shipping emissions, sea salt, soil dust and industrial emissions + biomass burning following in importance. Regarding source areas, the primary contributor of vehicle emissions was predominantly from the PRD region, whereas the coal combustion, aside from local contributions, also originates from the northern region. From a long-term perspective, NO3− pollution has remained relatively stable since the summer of 2020. Concurrently, coal combustion source has shown a localization trend. These insights derived from the extensive, high-frequency observation presented in this study serve as a valuable reference for devising strategies to control NO3− and PM2.5 in the PRD region and China.

Observation-Based Diagnostics of Reactive Nitrogen Recycling through HONO Heterogenous Production: Divergent Implications for Ozone Production and Emission Control.

Understanding of nitrous acid (HONO) production is crucial to photochemical studies, especially in polluted environments like eastern China. In-situ measurements of gaseous and particulate compositions were conducted at a rural coastal site during the 2018 spring Ozone Photochemistry and Export from China Experiment (OPECE). This data set was applied to investigate the recycling of reactive nitrogen through daytime heterogeneous HONO production. Although HONO levels increase during agricultural burning, analysis of the observation data does not indicate more efficient HONO production by agricultural burning aerosols than other anthropogenic aerosols. Box and 1-D modeling analyses reveal the intrinsic relationships between nitrogen dioxide (NO2), particulate nitrate (pNO3), and nitric acid (HNO3), resulting in comparable agreement between observed and simulated HONO concentrations with any one of the three heterogeneous HONO production mechanisms, photosensitized NO2 conversion on aerosols, photolysis of pNO3, and conversion from HNO3. This finding underscores the uncertainties in the mechanistic understanding and quantitative parametrizations of daytime heterogeneous HONO production pathways. Furthermore, the implications for reactive nitrogen recycling, ozone (O3) production, and O3 control strategies vary greatly depending on the HONO production mechanism. On a regional scale, the conversion of HONO from pNO3 can drastically enhance O3 production, while the conversion from NO2 can reduce O3 sensitivity to NOx changes in polluted eastern China.

Dissecting PM sensor capabilities: A combined experimental and theoretical study on particle sizing and physicochemical properties

Recent advancements in particulate matter (PM) optical measurement technology have enhanced the characterization of particle size distributions (PSDs) across various temporal and spatial scales, offering a more detailed analysis than traditional PM mass concentration monitoring. This study employs field experiments, laboratory tests, and model simulations to evaluate the influence of physicochemical characteristics of particulate matter (PM) on the performance of a compact, multi-channel PM sizing sensor. The sensor is integrated within a mini air station (MAS) designed to detect particles across 52 channels. The field experiments highlighted the sensor's ability to track hygroscopicity parameter κ-values across particle sizes, noting an increasing trend with particle size. The sensor's capability in identifying the size and mass concentration of different PM types, including ammonium nitrate, sodium chloride, smoke, incense, and silica dust particles, was assessed through laboratory tests. Laboratory comparisons with the Aerodynamic Particle Sizer (APS) showed high consistency (R2 > 0.96) for various PM sources, supported by Kolmogorov-Smirnov tests confirming the sensor's capability to match APSsize distributions. Model simulations further elucidated the influence of particle refractive index and size distributions on sensor performance, leading to optimized calibrant selection and application-specific recommendations. These comprehensive evaluations underscore the critical interplay between the chemical composition and physical properties of PM, significantly advancing the application and reliability of optical PM sensors in environmental monitoring.

Enhanced HONO Formation from Aqueous Nitrate Photochemistry in the Presence of Marine Relevant Organics: Impact of Marine-Dissolved Organic Matter (m-DOM) Concentration on HONO Yields and Potential Synergistic Effects of Compounds within m-DOM.

Nitrous acid (HONO) is a key molecule in the reactive nitrogen cycle. However, sources and sinks for HONO are not fully understood. Particulate nitrate photochemistry has been suggested to play a role in the formation of HONO in the marine boundary layer (MBL). Here we investigate the impact of marine relevant organic compounds on HONO formation from aqueous nitrate photochemistry. In particular, steady-state, gas-phase HONO yields were measured from irradiated nitrate solutions at low pH containing marine-dissolved organic matter (m-DOM). m-DOM induces a nonlinear increase in HONO yield across all concentrations compared to that for pure nitrate solutions, with rates of HONO formation increasing by up to 3-fold when m-DOM is present. Furthermore, to understand the potential synergistic effects that may occur within complex samples such as m-DOM, mixtures of chromophoric (light-absorbing) and aliphatic (non-light-absorbing) molecular proxies were utilized. In particular, mixtures of 4-benzoylbenzoic acid (4-BBA) and ethylene glycol (EG) in acidic aqueous solutions containing nitrate showed more HONO upon irradiation compared to solutions containing only one of the molecular proxies. This suggests that synergistic effects in the HONO formation can occur in complex organic samples. Atmospheric implications of the results presented here are discussed.

Modeling the Oxygen Isotope Anomaly (Δ17O) of Reactive Nitrogen in the Community Multiscale Air Quality Model: Insights into Nitrogen Oxide Chemistry in the Northeastern United States.

Atmospheric nitrate, including nitric acid (HNO3), particulate nitrate (pNO3), and organic nitrate (RONO2), is a key atmosphere component with implications for air quality, nutrient deposition, and climate. However, accurately representing atmospheric nitrate concentrations within atmospheric chemistry models is a persistent challenge. A contributing factor to this challenge is the intricate chemical transformations involving HNO3 formation, which can be difficult for models to replicate. Here, we present a novel model framework that utilizes the oxygen stable isotope anomaly (Δ17O) to quantitatively depict ozone (O3) involvement in precursor nitrogen oxides photochemical cycling and HNO3 formation. This framework has been integrated into the US EPA Community Multiscale Air Quality (CMAQ) modeling system to facilitate a comprehensive assessment of NO x oxidation and HNO3 formation. In application across the northeastern US, the model Δ17O compares well with recently conducted diurnal Δ17O(NO2) and spatiotemporal Δ17O(HNO3) observations, with a root mean square error between model and observations of 2.6 ‰ for Δ17O(HNO3). The model indicates the major formation pathways of annual HNO3 production within the northeastern US are NO+OH (46 %), N2O5 hydrolysis (34 %), and organic nitrate hydrolysis (12 %). This model can evaluate NO x chemistry in CMAQ in future air quality and deposition studies involving reactive nitrogen.

Synergistic effect of nitrocellulose coating on structural and reactivity stabilization of ammonium nitrate oxidizer

The present work aims to stabilize the room temperature allotropic transition of ammonium nitrate (AN) particles utilizing a microencapsulation technique, which involves solvent/non-solvent in which nitrocellulose (NC) has been employed as a coating agent. The SEM micrographs revealed distinct features of both pure AN and NC, contrasting with the irregular granular surface topography of the coated AN particles, demonstrating the adherence of NC on the AN surface. Structural analysis via infrared spectroscopy (IR) demonstrated a successful association of AN and NC, with slight shifts observed in IR bands indicating interfacial interactions. Powder X-ray Diffraction (PXRD) analysis further elucidated the structural changes induced by the coating process, revealing that the NC coating altered the crystallization pattern of its pure form. Thermal analysis demonstrates distinct profiles for pure and coated AN, for which the coated sample exhibits a temperature increase and an enthalpy decrease of the room temperature allotropic transition by 6 °C, and 36%, respectively. Furthermore, the presence of NC coating alters the intermolecular forces within the composite system, leading to a reduction in melting enthalpy of coated AN by ∼39% compared to pure AN. The thermal decomposition analysis shows a two-step thermolysis process for coated AN, with a significant increase in the released heat by about 78% accompanied by an increase in the activation barrier of NC and AN thermolysis, demonstrating a stabilized reactivity of the AN-NC particles. These findings highlight the synergistic effect of NC coating on AN particles, which contributed to a structural and reactive stabilization of both AN and NC, proving the potential application of NC-coated AN as a strategically advantageous oxidizer in composite solid propellant formulations.