Formation Of Ammonium Nitrate Research Articles

Fine particle concentrations and composition during wintertime inversions in Logan, Utah, USA

During Winter 2004, a series of elevated PM 2.5 events occurred in Logan, Utah, coinciding with strong winter inversions. This period resulted in 17 exceedances of the 24-h PM 2.5 standard, and some of the highest PM 2.5 mass loadings recorded in the United States, including 9 days of 24-h PM 2.5 measurements over 100 μg m −3. During the 3-month period, we monitored the size and mass concentrations of airborne particles using an aerosol mass spectrometer. PM 2.5 concentrations were dominated by the formation of ammonium nitrate, accounting for over 50% of the non-refractory aerosol matter throughout the study and 80% on the highest pollution days. Another 15–20% of the particulate matter was composed of organic carbon. The high particle concentration loadings in Utah's Cache Valley result from a combination of unfavorable meteorology dominated by a severe cold-temperature inversion, a mix of rural and urban emission sources, and a confined geographical area. As a rapidly growing formerly rural area, the Cache Valley is representative of future air pollution problems facing areas of the interior west undergoing rapid urbanization.

Wpływ wprowadzenia dolistnego nawożenia mikroelementami runi długotrwałego doświadczenia w Czarnym Potoku na zawartość wapnia

Basing on long-term fertilizer experiment localized on a mountain meadow (Czarny Potok near Krynica – 20o54’ E; 49o24’ N), the effect of treatment with Mikrovit-1 fertilizer on changes in the sward calcium concentrations was studied. The experiment set up in 1962 comprises 8 treatments and since 1985 it has been conducted in 0 CaO and +CaO series. Liming was repeated in 1985. Treatments with two doses of nitrogen (90 and 180 kg N ha-1) applied in two forms (ammonium nitrate and urea) against phosphorus-and-potassium fertilization provide the basis of the experiment. As a result of systematic mineral fertilization the meadow sward was characterized with very low content of calcium. For 18 years prior to liming the quantity of calcium taken up on NPK treatments had been almost twice bigger than in the period between the 18th and 36th year of the experiment. As a result of microelement fertilization applied in the 33rd year of the studies, sward calcium concentration increased in comparison with the four-year period preceding the measure application, which was particularly noticeable on treatment with incomplete NPK fertilization and in 2nd cut. Appli ed microelement fertilization more positively affected an increase in calcium concentrations in sward of the limed series than in the unlimed one. A lack of significant response to Mikrovit-1 fertilization on NPK treatments should be ascribed to very low doses of microelement fertilizer applied for conservative fertilization.

Processes Influencing Secondary Aerosol Formation in the San Joaquin Valley during Winter

Air quality data collected in the California Regional PM10/PM2.5 Air Quality Study (CRPAQS) are analyzed to qualitatively assess the processes affecting secondary aerosol formation in the San Joaquin Valley (SJV). This region experiences some of the highest fine particulate matter (PM2.5) mass concentrations in California (≤188 μg/m3 24-hr average), and secondary aerosol components (as a group) frequently constitute over half of the fine aerosol mass in winter. The analyses are based on 15 days of high-frequency filter and canister measurements and several months of wintertime continuous gas and aerosol measurements. The phase-partitioning of nitrogen oxide (NOx)-related nitrogen species and carbonaceous species shows that concentrations of gaseous precursor species are far more abundant than measured secondary aerosol nitrate or estimated secondary organic aerosols. Comparisons of ammonia and nitric acid concentrations indicate that ammonium nitrate formation is limited by the availability of nitric acid rather than ammonia. Time-resolved aerosol nitrate data collected at the surface and on a 90-m tower suggest that both the daytime and nighttime nitric acid formation pathways are active, and entrainment of aerosol nitrate formed aloft at night may explain the spatial homogeneity of nitrate in the SJV. NOx and volatile organic compound (VOC) emissions plus background O3 levels are expected to determine NOx oxidation and nitric acid production rates, which currently control the ammonium nitrate levels in the SJV. Secondary organic aerosol formation is significant in winter, especially in the Fresno urban area. Formation of secondary organic aerosol is more likely limited by the rate of VOC oxidation than the availability of VOC precursors in winter.

The Southeastern Aerosol Research and Characterization Study, Part 3: Continuous Measurements of Fine Particulate Matter Mass and Composition

Deployment of continuous analyzers in the Southeastern Aerosol Research and Characterization Study (SEARCH) network began in 1998 and continues today as new technologies are developed. Measurement of fine particulate matter (PM2.5) mass is performed using a dried, 30 °C tapered element oscillating microbalance (TEOM). TEOM measurements are complemented by observations of light scattering by nephelometry. Measurements of major constituents include: (1) SO4 2− via reduction to SO2; (2) NH4 + and NO3 − via respective catalytic oxidation and reduction to NO, (3) black carbon (BC) by optical absorption, (4) total carbon by combustion to CO2, and (5) organic carbon by difference between the latter two measurements. Several illustrative examples of continuous data from the SEARCH network are presented. A distinctive composite annual average diurnal pattern is observed for PM2.5 mass, nitrate, and BC, likely indicating the influence of traffic-related emissions, growth, and break up of the boundary layer and formation of ammonium nitrate. Examination of PM2.5 components indicates the need to better understand the continuous composition of the unmeasured “other” category, because it contributes a significant fraction to total mass during periods of high PM2.5 loading. Selected episodes are presented to illustrate applications of SEARCH data. An SO2 conversion rate of 0.2%/hr is derived from an observation of a plume from a coal-fired power plant during early spring, and the importance of local, rural sources of NH3 to the formation of ammonium nitrate in particulate matter (PM) is demonstrated.

Particulate sulphate and nitrate in Southern England and Northern Ireland during 2002/3 and its formation in a photochemical trajectory model

Daily measurements of sulphate and nitrate are reported from Harwell in southern England and Belfast in Northern Ireland for the period 2002/3. When the higher percentiles are compared with the mean concentration, nitrate reveals considerably greater episodicity than either sulphate or PM10 (measured by TEOM). A photochemical trajectory model using the Master Chemical Mechanism scheme has been used to predict daily concentrations of both nitrate and sulphate aerosol over the period March to August 2002 at the Belfast and Harwell sites. This has been carried out for daily samples using 72, 96 and 120 h air mass back trajectories obtained from both the British Atmospheric Data Centre and the HYSPLIT on-line service. Additionally, model simulations have been conducted for 5 trajectories generated through clustering of the trajectories for individual days. This reveals an under-prediction of the model associated particularly with trajectories originating from the European mainland. In general, the model performs reasonably well in simulating concentrations of both nitrate and sulphate, which is surprising given that the model does not account for processes requiring the presence of liquid water. This suggests that aqueous phase oxidation processes may not make a major contribution to airborne sulphate concentrations in the U.K. in the spring and summer months. It appears that inclusion of explicit ammonium nitrate formation chemistry may be essential to reliable prediction of episodic nitrate peaks.

Influence of NO2 on the hydrolysis of isocyanic acid over TiO2

Investigation of the catalytic hydrolysis of isocyanic acid (HNCO) over TiO2 revealed that the rate of hydrolysis was considerably reduced in the presence of NO2 at temperatures below 200°C. Transient low temperature investigations of the reaction, Temperature Programmed Desorption (TPD) experiments and Diffuse Reflectance Infrared Fourier Transform (DRIFT) investigations showed that part of the NO2 adsorbed strongly on the surface while part reacted with NH3 to form ammonium nitrate on the catalyst surface. Since at high temperatures NO2 was desorbed and NH4NO3 was decomposed, the catalytic activity was completely restored by thermal treatment at high temperature.

Toward Improved Catalytic Low-Temperature NOx Removal in Diesel-Powered Vehicles

The potential of different catalytic after treatment techniques to meet future diesel emission standards, which are strongly shifted toward urban driving conditions including cold start, are critically discussed in this Account and evaluated for their suitability for commercial applications. The dominating techniques in this field are NO(x) storage, urea-selective catalytic reduction (SCR), and HC-SCR. Each of these techniques have significant disadvantages such as sulfur sensitiveness and regeneration requirements of NO(x)-storage materials, infrastructure issues and formation of ammonium nitrate (at low temperatures) for urea-SCR, and low-temperature activity of HC-SCR catalysts. Ways to overcome these disadvantages in commercial applications may involve optimized regeneration strategies, reactor modifications, flow reversal, closed-loop NO(x) feedback systems, nonthermal plasma, and/or hydrogen-assisted catalyses, etc.

Comparison of PM2.5 and PM10 in A Suburban Area in Korea During April, 2003

Airborne particulate matter (PM) concentrations were measured in Iksan, a suburban area in South Korea during April, 2003. PM2.5 (particles with an aerodynamic diameter less than 2.5 μm) and PM10 (particles with an aerodynamic diameter less than 10 μm) samples were collected, and the chemical characteristics of particles were examined for diurnal patterns, yellow dust/rainfall influences, and scavenging effects. Average concentrations of PM2.5 and PM10 mass measured were 37.3 ± 16.2 μg m−3 and 60.8 ± 29.5 μg m−3, respectively. The sum of ionic chemical species concentrations for PM2.5 and PM10 was 16.9 ± 7.3 and 23.1 ± 10.1 μg/m3, respectively. A significant reduction in PM mass concentrations during rainfall days was observed for coarse mode (PM2.5 − 10) particles, but less reduction was found for fine (PM2.5) mass concentration. SO42−, NH4+, and K+ predominated in fine particulate mode, NO3− and Cl− predominated in fine particle mode and coarse particle mode, but Na+, Mg2+, and Ca2+ mostly existed in coarse mode. The high concentration of ammonium due to local emissions and long-range transport neutralized sulfate and nitrate to ammonium sulfate and ammonium nitrate, which were major forms of airborne PM in Iksan. Average mass concentrations of PM10 in daytime and at night were 57.6 and 70.0 μg m−3, and those of PM2.5 were 35.4 and 42.5 μg m−3, respectively. NO3− and Cl− in both PM2.5 and PM10 were about double at night than in the daytime, while the rest of the chemical species were equal or a little higher at night than in the daytime. The results suggest the formation of ammonium nitrate and chloride when high ammonia concentration and low air temperature are allowed. Backward air trajectory analyses showed that air masses arriving at the site during yellow dust period were transported from arid Chinese regions, which resulted in high concentrations of airborne PM mass concentrations. In the meantime, air mass trajectories during a rainfall period were mostly from the Pacific Ocean or the East China Sea, along with a relatively low PM concentration.

Control strategies for the reduction of airborne particulate nitrate in California's San Joaquin Valley

Abstract The effect of NO x , volatile organic compound (VOC), and NH 3 emissions control programs on the formation of particulate ammonium nitrate in the San Joaquin Valley (SJV) was examined under the typical winter conditions that existed on 4–6 January, 1996. The UCD/CIT photochemical transport model was used for this study so that the source origin of primary particulate matter and secondary particulate matter could be identified. When averaged across the entire SJV, the model results predict that 13–18% of the reactive nitrogen (NO y =NO x +reaction products of NO x ) emitted from local sources within the SJV was converted to nitrate at the ground level. Each gram of NO x emitted locally within the SJV (expressed as NO 2 ) produced 0.23–0.31 g of particulate ammonium nitrate (NH 4 NO 3 ), which is much smaller than the maximum theoretical yield of 1.7 g of NH 4 NO 3 per gram of NO 2 . The fraction of reactive nitrogen converted to nitrate varied strongly as a function of location. Urban regions with large amounts of fresh NO emissions converted little reactive nitrogen to nitrate, while remote areas had up to 70% conversion (equivalent to approximately 1.2 g of NH 4 NO 3 per gram of NO 2 ). The use of a single spatially averaged ratio of NH 4 NO 3 /NO x as a predictor of how changes to NO x emissions would affect particulate nitrate concentrations would not be accurate at all locations in the SJV under the conditions studied. The largest local sources of particulate nitrate in the SJV were predicted to be diesel engines and catalyst equipped gasoline engines under the conditions experienced on 6 January, 1996. Together, these sources accounted for less than half of the ground-level nitrate aerosol in the SJV. The remaining fraction of the aerosol nitrate originated from reactive nitrogen originally released upwind of the SJV. The majority of this upwind reactive nitrogen was already transformed to nitrate by the time it entered the SJV. The effect of local emissions controls on this upwind material was small. A 50% reduction in NO x emissions applied to sources within the SJV reduced the predicted concentration of total nitrate by approximately 25% during the study episode. VOC emissions controls were less effective, while reasonable NH 3 emissions controls had the smallest effect on the amount of ammonium nitrate produced. A 50% reduction in VOC emissions lowered predicted concentrations of total nitrate by 17.5%, while a 50% reduction in NH 3 emissions lowered predicted concentrations of total nitrate by only 10%. This latter result is expected since the formation of ammonium nitrate aerosol is limited by the availability of gas-phase nitric acid, with large amounts of excess NH 3 available. NO x emissions controls appear to be the most efficient method to reduce the concentration of locally generated particulate nitrate in the SJV under the conditions experienced on 4–6 January, 1996.

Correction to “Effect of Reaction Temperature on<tex>$hboxNO_x$</tex>Removal and Formation of Ammonium Nitrate in Nonthermal Plasma Process Combined With Selective Catalytic Reduction”

Correction to “Effect of Reaction Temperature on<tex>$hboxNO_x$</tex>Removal and Formation of Ammonium Nitrate in Nonthermal Plasma Process Combined With Selective Catalytic Reduction”

Aerosol Ion Characteristics During the Big Bend Regional Aerosol and Visibility Observational Study

The ionic compositions of particulate matter with aerodynamic diameter ≤2.5 μm (PM2.5) and size-resolved aerosol particles were measured in Big Bend National Park, Texas, during the 1999 Big Bend Regional Aerosol and Visibility Observational study. The ionic composition of PM2.5 aerosol was dominated by sulfate (SO4 2−) and ammonium (NH4 +). Daily average SO4 2− and NH4 + concentrations were strongly correlated (R2 = 0.94). The molar ratio of NH4 + to SO4 2− averaged 1.54, consistent with concurrent measurements of aerosol acidity. The aerosol was observed to be comprised of a submicron fine mode consisting primarily of ammoniated SO4 2− and a coarse particle mode containing nitrate (NO3 −). The NO3 − appears to be primarily associated with sea salt particles where chloride has been replaced by NO3 −, although formation of calcium nitrate (Ca(NO3)2) is important, too, on several days. Size-resolved aerosol composition results reveal that a size cut in particulate matter with aerodynamic diameter ≤1 μm would have provided a much better separation of fine and coarse aerosol modes than the standard PM2.5 size cut utilized for the study. Although considerable nitric acid exists in the gas phase at Big Bend, the aerosol is sufficiently acidic and temperatures sufficiently high that even significant future reductions in PM2.5 SO4 2− are unlikely to be offset by formation of particulate ammonium nitrate in summer or fall.

Effect of Reaction Temperature on NO<tex>$_x$</tex>Removal and Formation of Ammonium Nitrate in Nonthermal Plasma Process Combined With Selective Catalytic Reduction

This study investigated nonthermal plasma process combined with monolithic V/sub 2/O/sub 5//TiO/sub 2/ catalyst for the removal of nitrogen oxides. The combination process was made in either one-stage (generation of plasma inside catalyst) or two-stage process (plasma reactor, followed by catalyst) in order to understand the role of nonthermal plasma. It was shown that nonthermal plasma does not activate catalyst, but merely changes the gas composition, especially NO and NO/sub 2/ concentrations. The effect of reaction temperature on the removal of NO/sub x/ and the formation of ammonium nitrate was examined to find out an appropriate operating condition. The formation of ammonium nitrate on catalyst surface that is the main cause of catalyst deactivation was identified by scanning electron microscope images. As a result of the change in the gas composition by the nonthermal plasma, the combination process allowed high NO/sub x/ removal efficiency at relatively low temperatures below 200/spl deg/C. For the present process, the NO/sub x/ removal efficiency obtained in the range of 75/spl deg/C-200/spl deg/C was around 80%, which corresponds to an energy yield of 48 eV/NO/sub x/-molecule removed. It was found that the combination process should be operated above 170/spl deg/C to prevent ammonium nitrate from forming.

A “Nitrate Route” for the low temperature “Fast SCR” reaction over a V2O5–WO3/TiO2commercial catalyst

A novel mechanism is proposed for the Fast SCR reaction of NH(3), NO and NO(2) at low temperature involving the formation of ammonium nitrate as intermediate and its subsequent reaction with NO as the rate determining step.

Variability in ammonium nitrate formation and nitric acid depletion with altitude and location over California

Spatial variations in the partitioning of nitrate between gas phase nitric acid (HNO3) and particulate ammonium nitrate were observed using airborne measurements of trace gas mixing ratios, particle size distributions, and particle composition. During the Intercontinental Transport and Chemical Transformation experiment in April and May 2002 the NOAA WP‐3 aircraft flew up to 8 km altitude on 11 research flights from Monterey, California. The formation of semivolatile aerosols was studied by examining the enhancement of fine‐particulate ammonium nitrate and depletion of gas‐phase HNO3 over the San Joaquin Valley, Los Angeles Basin, and Mojave Desert. Gas‐phase particle precursors, HNO3 and ammonia (NH3), were converted to particulate ammonium nitrate at higher altitudes within the boundary layer. These particle layers were a consequence of lower ambient temperatures that caused a reduction of the dissociation constant for ammonium nitrate aerosol so that gas phase HNO3 was depleted and particle mass was formed. The resulting vertical gradients in particulate matter and HNO3 were observed in well‐mixed boundary layers where other directly emitted trace gases (CO) and secondary pollutants (O3) exhibited no vertical gradients. Hence the equilibrium between the gas and particle phases occurred faster than boundary layer mixing times and chemical rather than meteorological effects were responsible for the layers of enhanced particulate matter aloft. Coincident HNO3 depletion and ammonium nitrate formation was also observed downwind from regions characterized by large agricultural NH3 emissions in the Los Angeles Basin and San Joaquin Valley.

Evaluation and improvement of ammonia emissions inventories

Abstract Two case studies are performed to improve ammonia emissions inputs used to model fine particulate matter (PM2.5 is the portion of particulate matter smaller than 2.5 μm aerodynamic diameter) formation of ammonium sulfate and ammonium nitrate. Ammonia emissions are analyzed in detail for North Carolina and the San Joaquin Valley (SJV) of California, with a focus on the Charlotte, NC, and Fresno, California metropolitan areas. A new gridded ammonia emissions inventories suitable for atmospheric modeling for the two case study cities was also developed. Agricultural sources accounted for the bulk of ammonia emissions in both case studies. Livestock waste contributed about 80% in North Carolina and 64% in the SJV, while fertilizer application contributed about 6–7% in both domains. Forests and non-agricultural vegetation contributed 5% in North Carolina and 12% in the SJV. Motor vehicles accounted for about 6% of ammonia emissions in North Carolina and 14% in the SJV. In the Charlotte and Fresno urban areas, the distribution of emissions is less heavily weighted toward agricultural sources and more heavily weighted toward highway vehicles (highway vehicles account for an estimated 64% of emissions in Charlotte and 51% of emissions in Fresno). The emissions estimates for agricultural sources (livestock and fertilizer application) decline to approximately 14% in the winter for both the Charlotte and Fresno urban areas. Emissions estimates for soils and vegetation also decline to approximately 0 during the winter for both the Fresno and Charlotte area. As a result, motor vehicles account for a larger fraction (approximately 73% and 70% for Charlotte and Fresno, respectively) of winter ammonia emissions, particularly in the Charlotte urban area.

The Treasure Valley secondary aerosol study I: measurements and equilibrium modeling of inorganic secondary aerosols and precursors for southwestern Idaho

The SCAPE2 aerosol equilibrium model was applied to measured concentrations of PM 2.5 aerosol and precursor gases. Ambient measurements in the Treasure Valley, Idaho were collected during stagnation episodes between December 1999 and March 2000 when conditions were favorable for the formation of secondary inorganic aerosol. SCAPE2 results agreed well with measurements for the episodes tested; Monte Carlo simulation using the uncertainties of the model input variables indicated that discrepancies between measured and modeled results were within the range of analytical precision. Air pollution control strategies were evaluated by perturbing the model input concentrations of total sulfate, nitrate, and ammonium. The largest reductions in secondary aerosol concentrations occurred when total nitrate was reduced, indicating that the formation of ammonium nitrate was limited by the availability of nitrate.

Atmospheric concentrations of ammonia and ammonium at an agricultural site in the southeast United States

In this study, we present ∼1 yr (October 1998–September 1999) of 12-hour mean ammonia (NH 3), ammonium (NH 4 +), hydrochloric acid (HCl), chloride (Cl −), nitrate (NO 3 −), nitric acid (HNO 3), nitrous acid (HONO), sulfate (SO 4 2−), and sulfur dioxide (SO 2) concentrations measured at an agricultural site in North Carolina's Coastal Plain region. Mean gas concentrations were 0.46, 1.21, 0.54, 5.55, and 4.15 μg m −3 for HCl, HNO 3, HONO, NH 3, and SO 2, respectively. Mean aerosol concentrations were 1.44, 1.23, 0.08, and 3.37 μg m −3 for NH 4 +, NO 3 −, Cl −, and SO 4 2−, respectively. Ammonia, NH 4 +, HNO 3, and SO 4 2− exhibit higher concentrations during the summer, while higher SO 2 concentrations occur during winter. A meteorology-based multivariate regression model using temperature, wind speed, and wind direction explains 76% of the variation in 12-hour mean NH 3 concentrations ( n=601). Ammonia concentration increases exponentially with temperature, which explains the majority of variation (54%) in 12-hour mean NH 3 concentrations. Dependence of NH 3 concentration on wind direction suggests a local source influence. Ammonia accounts for >70% of NH x (NH x =NH 3+NH 4 +) during all seasons. Ammonium nitrate and sulfate aerosol formation does not appear to be NH 3 limited. Sulfate is primarily associated ammonium sulfate, rather than bisulfate, except during the winter when the ratio of NO 3 −–NH 4 + is ∼0.66. The annual average NO 3 −–NH 4 + ratio is ∼0.25.

Livestock ammonia management and particulate-related health benefits.

Agricultural operations are the largest source of ammonia emissions in the United States and contribute to the formation of ammonium nitrate and ammonium sulfate, two prevalent forms of fine particulate matter. Researchers have found an association between fine particulate matter and a variety of adverse healths effects, including premature mortality, chronic bronchitis, hospital admissions, and asthma attacks. Management practices that reduce ammonia emissions may decrease adverse health effects, resulting in significant economic benefits. We estimated the impact of a variety of emission controls, including diet optimization, alum, and incorporation of manure into the land. The results suggest that relatively modest management policies can have a significant impact on fine particulate formation in the atmosphere. Because of the heterogeneous nature of particulate matter, a key question is the importance of particulate matter size and composition. To the extent that ammonium nitrate and ammonium sulfate contribute to adverse health effects, ammonia management may have significant health implications. Our results suggestthat a 10% reduction in livestock ammonia emissions can lead to over $4 billion annually in particulate-related health benefits.

Selective catalytic reduction of NO and NO 2 at low temperatures

The fast SCR reaction using equimolar amounts of NO and NO 2 is a powerful means to enhance the NO x conversion over a given SCR catalyst. NO 2 fractions in excess of 50% of total NO x should be avoided because the reaction with NO 2 only is slower than the standard SCR reaction. At temperatures below 200 °C, due to its negative temperature coefficient, the ammonium nitrate reaction gets increasingly important. Half of each NH 3 and NO 2 react to form dinitrogen and water in analogy to a typical SCR reaction. The other half of NH 3 and NO 2 form ammonium nitrate in close analogy to a NO x storage-reduction catalyst. Ammonium nitrate tends to deposit in solid or liquid form in the pores of the catalyst and this will lead to its temporary deactivation. The various reactions have been studied experimentally in the temperature range 150–450 °C for various NO 2/NO x ratios. The fate of the deposited ammonium nitrate during a later reheating of the catalyst has also been investigated. In the absence of NO, the thermal decomposition yields mainly ammonia and nitric acid. If NO is present, its reaction with nitric acid on the catalyst will cause the formation of NO 2.

Sensitivity of particulate matter nitrate formation to precursor emissions in the California San Joaquin Valley.

The formation of secondary ammonium nitrate during the 1995 Integrated Monitoring Study (IMS95) in San Joaquin Valley, CA was investigated using a box model that simulates the atmospheric chemistry and gas/particle partition of inorganic compounds. The concentration of particulate matter (PM) nitrate was found to be sensitive to reductions in VOC emissions. Nitric acid, rather than ammonia, was the limiting reagent in the formation of PM nitrate. The formation of nitric acid was more sensitive to the availability of oxidants than that of NOx. Oxidant chemistry in wintertime conditions in the San Joaquin Valley was shown to be VOC-sensitive. In fact, a decrease in NOx emissions may have the counter-intuitive effect of increasing PM nitrate.