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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Non-sea-salt sulfate and methanesulfonate at American Samoa

High-volume bulk aerosol samples have been collected at American Samoa (14.25 deg S, 170.58 deg W) on a semicontinuous basis since the system was erected as part of the Sea/Air Exchange Program (SEAREX) in March 1983. In this report we consider those samples collected through May 6, 1992. For most of this period the sample filters were changed once a week. However, during November 1989 and from May 10 to June 10, 1990, in conjunction with the aircraft missions of the NASA Global Backscatter Experiment (GLOBE), the filters were changed daily. All of the samples were analyzed for nonsea-salt (nss) SO4(2-) and NO3(-). Analyses for methanesulfonate (MSA) include all of the 53 daily samples, 22 weekly samples from March 19, 1983, through April 12, 1984, and 96 weekly samples from January 3, 1990, through May 6, 1992. The mean concentrations (in micrograms per cubic meter) were 0.37 for nss SO4(2-), 0.0229 for MSA, 0.114 for NO3(-), and 5.1 for Na(+). Nss SO4(2-) and MSA are strongly linearly correlated in these 171 samples (r(exp 2) = 0.66) and the regression intercept does not differ significantly from zero. The geometric mean (GM) nss SO4(2-)/MSA ratio, 18.1 +/- 0.9 (where +/- indicates the 95% confidence interval of the GM) is about 7% higher than had previously been reported for this station. The ratio exhibits no significant seasonal variation. Although the ratio appeared to be significantly lower in the May - June 1990 daily samples (GM = 15.3 +/- 1.2), a further examination of the results indicated that the variance of the measured ratios from 18.1 (the GM for the whole data set) was attributable almost exclusively to the typical random errors in the analyses as determined from the 1 sigma analytical uncertainties of 5% for MSA and SO4(2-) and 2% for Na(+).

Savoie, Dennis L.↗
NASA NTRS1992

Soil Dynamics Following Fire in Juncus and Spartina Marshes

We examined soil changes in the O-5 and 5-15 cm layers for one year after a fire in burned Juncus roemerianus and Spartina bakeri marshes and an unburned Juncus marsh. Each marsh was sampled (N = 25) preburn, immediately postburn, and 1, 3, 6, 9, and 12 months postburn. All marshes were flooded at the time of the fire; water levels declined below the surface by 6 months but reflooded at 12 months after the fire. Soil samples were analyzed for pH, conductivity, organic matter, exchangeable Ca, Mg, and K, available PO4-P, total Kjeldahl nitrogen (TKN), exchangeable NO3-N, NO2-N, and NH4-N. Changes due to burning were most pronounced in the surface (0-5 cm) layer. Soil pH increased 0.16-0.28 units immediately postburn but returned to preburn levels in 1 month. Organic matter increased by 1 month and remained elevated through 9 months after the fire. Calcium, Mg, K, and PO4-P all increased by 1 month after burning, and the increases persisted for 6 to 12 months. Conductivity increased in association with these cations. Burning released ions from organic matter as indicated by the increase in pH, conductivity, Ca, Mg, K, and PO4-P. NH4-N in burned marshes was elevated 6 months and NO3-N 12 months after burning. TKN showed seasonal variations but no clear fire-related changes. Nitrogen species were affected by the seasonally varying water levels as well as fire; these changes differed from those observed in many upland systems.

Schmalzer, Paul A.↗
NASA NTRS1997

The Kinetic Nonequilibrium Processes in the Internal Flow and in the Plume of Subsonic and Supersonic Aircrafts

(1) Our results show that under combustion of thermal destruction products of n-C8H18, and other hydrocarbon fuels with air at the equivalent ratio -0.5 and less the chemical equilibrium is not realized at the exit plane of combustion chamber and in the gas turbine and nozzle for most of small components such as NO2, NO3, HNO, HNO2, HNO3, N(x)H(y), HO2, OH. The chemical equilibrium is not realized in the internal flow of ramjet hydrogen combustion engine too. So at the nozzle exit plane both of gas-turbine hydrocarbon combustion engine and of ramjet hydrogen combustion engine the relatively large values of concentration of such small components as NO3, HNO2, N2O, HNO3, HNO, NH, N2H, HO2, H2O2 may be realized. The exact definition of these component concentration as well as concentration of NO(x), OH, SO2, O, H, H2, H2O at the nozzle exit plane is very important for plume chemistry. (2) The results which were obtained for subsonic and hypersonic aircrafts indicate on the considerable change of the composition of the gas mixture along the plume. This change can be caused not only by the mixture of combustion products with the atmosphere air but by proceeding of whole complex of nonequilibrium photochemical reactions. The photodissociation processes begin to influence on the formation of the free atoms and radicals at flight altitude H greater than or equal to 18 km. Neglect of these processes can result in essential (up to 10(exp 4) times) mistakes of values gamma(sub OH), gamma(sub O), gamma(sub H), gamma(sub HSO3) and some products of CFC's disintegration. It was found that penetration of Cl-containing species from the atmosphere into the exhaust flow and its interaction with nitrogen oxides leads to essential increasing of the concentration of Cl, Cl2, ClO2, ClNO3, CH3Cl and sometimes HCl and the decreasing of ClO concentration by comparison with background values. The results of our analysis show that the plume aircraft with both hydrocarbon and hydrogen combustion engine may be source of various pollutant components such as HNO, HNO4,ClO2, CH3NO2, CH3NO3, CH2O, Cl, H2O2, but not only NO, NO2, HNO2, HNO3, N2O5, SO2, SO3, H2SO4 as it was supposed before.

Starik, Alexander M.↗
NASA NTRS1997

Kinetics of the Reactions of F((sup 2)P) and Cl((sup 2)P) with HNO3

The kinetics of the reactions of HNO3 with fluorine (k(sub 1)) and Chlorine (k(sub 2)) atoms have been studied by using a time-resolved long-path laser absorption technique to monitor the appearance of product NO3 radicals following 351-nm pulsed laser photolysis of X2/HNO3/He mixtures (X = F,Cl). Absolute rate coefficients for the F((sup 2)P) + HNO reaction have been determined over the temperature range 260-373 K. Between 260 and 320 K, the data are adequately represented by the Arrhenius expression k(sub 1)(T) = (6.0 +/- 2.6) x 10(exp -12) exp[(40 +/- 120)/T]cu cm/(molecule.s). Between 335 and 373 K, the rate coefficient is found to be (2.0 +/- 0.3) x 10(exp -11)cu cm/(molecule.s) independent of temperature. The observed temperature dependence suggests that reaction proceeds via competing direct abstraction and complex pathways. No NO3 production was observed in the experiments with X equals Cl, thus establishing that k(sub 2)(298 K) is less than 2 x 10(exp -16) cu cm/(molecule.s). The Cl((sup 2)P) + HNO reaction was also investigated by using a pulsed laser photolysis-resonance fluorescence technique to monitor the decay of Cl((sup 2)P). Upper limit values for k(sub 2) obtained from these experiments, in units of 10(exp -16)cu cm/(molecule.s), are 13 at 298 K and 10 at 400 K.

Wine, P. H.↗
NASA NTRS1999

Population of Nitrifying Bacteria and Nitrification in Ammonium Saturated Clinoptilolite

As humans begin to spend longer periods of time in space, plants will be incorporated into life support systems. Ammonium saturated clinoptilolite is one plant growth substrate but a balance between ammonium and nitrate is needed. A laboratory study was conducted to determine effects of nitrifying bacteria on ammonium concentrations and kinetics of nitrification. Columns containing clinoptilolite substrate amended with nitrifying bacteria obtained from soil enrichment were analyzed weekly for a 90 day period. The enrichment culture initially contained 1 x 10(exp 5) ammonium oxidizing bacteria and 1 x 10(exp 2) nitrite oxidizing bacteria per gram of substrate. Populations of ammonium oxidizing bacteria increased to 1 x 10(exp 6) and nitrite oxidizing bacteria increased to 1 x 10(exp 3) per gram of substrate. The nitrification rate was approximately 0.25mg NO3(-)-N/kg.hr. Experiments were also conducted to enumerate nitrifying bacteria in a clinoptilolite substrate used to grow wheat (Triticum aestivum L.). Seventy days following the initial inoculation with an unknown number of commercial nitrifying bacteria, 1 x 10(exp 5) ammonium oxidizing bacteria per gram of substrate were present. The number of nitrite oxidizing bacteria was between 1 x 10(exp 3) to 10(exp 4) per gram of substrate as measured by the most probable number method. Nitrification rates were approximately 0.20mg NO3(-)-N/kg.hr. Clinoptilolite readily exchanged sufficient concentrations of ammonium to support nitrifying bacteria and they survived well in this medium.

McGilloway, R. L.↗
NASA NTRS1997

Barium Nitrate Raman Laser Development for Remote Sensing of Ozone

In order to understand the impact of anthropogenic emissions upon the earth's environment, scientists require remote sensing techniques which are capable of providing range-resolved measurements of clouds, aerosols, and the concentrations of several chemical constituents of the atmosphere. The differential absorption lidar (DIAL) technique is a very promising method to measure concentration profiles of chemical species such as ozone and water vapor as well as detect the presence of aerosols and clouds. If a suitable DIAL system could be deployed in space, it would provide a global data set of tremendous value. Such systems, however, need to be compact, reliable, and very efficient. In order to measure atmospheric gases with the DIAL technique, the laser transmitter must generate suitable on-line and off-line wavelength pulse pairs. The on-line pulse is resonant with an absorption feature of the species of interest. The off-line pulse is tuned so that it encounters significantly less absorption. The relative backscattered power for the two pulses enables the range-resolved concentration to be computed. Preliminary experiments at NASA LaRC suggested that the solid state Raman shifting material, Ba(NO3)2, could be utilized to produce these pulse pairs. A Raman oscillator pumped at 532 nm by a frequency-doubled Nd:YAG laser can create first Stokes laser output at 563 nm and second Stokes output at 599 nm. With frequency doublers, UV output at 281 nm and 299 nm can be subsequently obtained. This all-solid state system has the potential to be very efficient, compact, and reliable. Raman shifting in Ba(NO3)2, has previously been performed in both the visible and the infrared. The first Raman oscillator in the visible region was investigated in 1986 with the configurations of plane-plane and unstable telescopic resonators. However, most of the recent research has focused on the development of infrared sources for eye-safe lidar applications.

McCray, Christopher L.↗
NASA NTRS2004

Rapid Measurements of Aerosol Ionic Composition and 3-10 nm Particle Size Distributions On The NASA P3 To Better Quantify Processes Affecting Aerosols Advected From East Asia

The Particle Into Liquid Sample (PILS) was deployed on the NASA P3 for airborne measurements of fine particle ionic chemical composition. The data have been quality assured and reside in the NASA data archive. We have analyzed our data to characterize the sources and atmospheric processing of fine aerosol particles advected from the region during the experiments. Fine particle water-soluble potassium was found to serve as a useful aerosol tracer for biomass smoke. Ratios of PILS potassium to sulfate are used as a means of estimating the percent contribution of biomass burning to fine particle mass in mixed plumes advecting from Asia. The high correlations between K+ and NO3(sup -) and NH4(sup +)' indicated that biomass burning was a significant source of these aerosol compounds in the region. It is noteworthy that the air mass containing the highest concentrations of fine particles recorded in all of ACE-Asia and TRACE-P appeared to be advecting from the Bejing/Tientsin urban region and also had the highest K(+), NO3(sup -) and NH4(sup +) concentrations of both studies. Based on K+/SO4(sup 2-) ratio's, we estimated that the plume was composed of approx. 60% biomass burning emissions, possibly from the use of bio-fuels in the urban regions.

Weber, Rodney J.↗
NASA NTRS2003

Nitrification in a zeoponic substrate

Clinoptilolite is a zeolite mineral with high cation exchange capacity used in zeoponic substrates that have been proposed as a solid medium for growing plants or as a fertilizer material. The kinetics of nitrification has not been measured for NH4+ saturated zeoponic substrate. Experiments were conducted to evaluate the production of NO2- and NO3-, and nitrifier populations in zeoponic substrates. Small columns were filled with zeoponic substrate inoculated with a commercial inoculum or soil enrichment culture of nitrifying bacteria. In addition to column studies, a growth chamber study was conducted to evaluate the kinetics of nitrification in zeoponic substrates used to grow radishes (Raphanus sativus L.). The zeoponic substrate provided a readily available source of NH4+, and nitrifying bacteria were active in the substrate. Ammonium oxidation rates in column studies ranged from 5 to 10 micrograms N g-1 substrate h-1, and NO2- oxidation rates were 2 to 9.5 micrograms N g-1 substrate h-1. Rates determined from the growth chamber study were approximately 1.2 micrograms N g-1 substrate h-1. Quantities of NH4+ oxidized to NO2- and NO3- in inoculated zeoponic substrate were in excess of plant up-take. Acidification as a result of NH4+ oxidation resulted in a pH decline, and the zeoponic substrate showed limited buffering capacity.

NASA Discipline Life Support Systems↗
NASA NTRS1990

Somatic embryogenesis of carrot in hormone-free medium: external pH control over morphogenesis

Cultures of preglobular stage proembryos (PGSPs) were initiated from mechanically wounded mature zygotic embryos of carrot, Daucus carota, on a hormone-free, semisolid medium. These PGSPs have been maintained and multiplied for extended periods without their progression into later embryo stages on the same hormone-free medium containing 1 mM NH4+ as the sole nitrogen source. Sustained maintenance of cultures comprised exclusively of PGSPs was dependent on medium pH throughout the culture period. Best growth and multiplication of PGSP cultures occurred when the pH of unbuffered, hormone-free medium fell from 4.5 to 4 over a 2-week period or when buffered medium was titrated to pH 4. If the hormone-free medium was buffered to sustain a pH at or above 4.5, PGSPs developed into later embryo stages. Maintenance with continuous multiplication of PGSPs occurred equally well on medium containing NH4+ or NH4+ and NO3-, but growth was poor with NO3- alone. Additional observations on the effects of medium components such as various nitrogen sources and levels, sucrose concentration, semisolid supports, type of buffer, borate concentration, activated charcoal, and initial pH that permit optimum maintenance of the PGSPs or foster their continued developmental progression into mature embryos and plantlets are reported. The influence of the pH of the hormone-free medium as a determinant in maintaining cultures as PGSPs or allowing their continued embryonic development are unequivocally demonstrated by gross morphology, scanning electron microscopy, and histological preparations.

NASA Discipline Number 29-20↗
NASA NTRS1989

Cyclic variations in nitrogen uptake rate of soybean plants: ammonium as a nitrogen source

When NO3- is the sole nitrogen source in flowing solution culture, the net rate of nitrogen uptake by nonnodulated soybean (Glycine max L. Merr. cv Ransom) plants cycles between maxima and minima with a periodicity of oscillation that corresponds with the interval of leaf emergence. Since soybean plants accumulate similar quantities of nitrogen when either NH4+ or NO3- is the sole source in solution culture controlled at pH 6.0, an experiment was conducted to determine if the oscillations in net rate of nitrogen uptake also occur when NH4+ is the nitrogen source. During a 21-day period of vegetative development, net uptake of NH4+ was measured daily by ion chromatography as depletion of NH4+ from a replenished nutrient solution containing 1.0 millimolar NH4+. The net rate of NH4+ uptake oscillated with a periodicity that was similar to the interval of leaf emergence. Instances of negative net rates of uptake indicate that the transition between maxima and minima involved changes in influx and efflux components of net NH4+ uptake.

NASA Discipline Life Support Systems↗
NASA NTRS1991

Soluble carbohydrate allocation to roots, photosynthetic rate of leaves, and nitrate assimilation as affected by nitrogen stress and irradiance

Upon resupply of exogenous nitrogen to nitrogen-stressed plants, uptake rate of nitrogen is enhanced relative to nonstressed plants. Absorption of nitrogen presumably is dependent on availability of carbohydrates in the roots. A buildup in soluble carbohydrates thus should occur in roots of nitrogen-stressed plants, and upon resupply of exogenous nitrogen the increased uptake rate should be accompanied by a rapid decline in carbohydrates to prestress levels. To evaluate this relationship, three sets of tobacco plants growing in a complete hydroponic solution containing 1.0 mM NO3- were either continued in the complete solution for 21 d, transferred to a minus-nitrogen solution for 21 d, or transferred to a minus-nitrogen solution for 8-9 d and then returned to the 1.0 mM NO3- solution. These nitrogen treatments were imposed upon plants growing at photosynthetic photon flux densities of 700 and 350 micromoles m-2 s-1. Soluble carbohydrate levels in roots increased during onset of nitrogen stress to levels that were fourfold greater than in roots of non-stressed plants. Following resupply of external nitrogen, a rapid resumption of nitrogen uptake was accompanied by a decline in soluble carbohydrates in roots to levels characteristic of nonstressed plants. This pattern of soluble carbohydrate levels in roots during onset of and recovery from nitrogen stress occurred at both irradiance levels. The response of net photosynthetic rate to nitrogen stress could be expressed as a nonlinear function of concentration of reduced nitrogen in leaves. The net photosynthetic rate at a given concentration of reduced nitrogen, however, averaged 10% less at the lower than at the higher irradiance. The decline in net photosynthetic rate per unit of reduced nitrogen in leaves at the lower irradiance was accompanied by an increase in the nitrate fraction of total nitrogen in leaves from 20% at the higher irradiance to 38% at the lower irradiance.

NASA Discipline Number 61-10↗
NASA NTRS2000

Biological removal of gaseous ammonia in biofilters: space travel and earth-based applications

Gaseous NH3 removal was studied in laboratory-scale biofilters (14-L reactor volume) containing perlite inoculated with a nitrifying enrichment culture. These biofilters received 6 L/min of airflow with inlet NH3 concentrations of 20 or 50 ppm, and removed more than 99.99% of the NH3 for the period of operation (101, 102 days). Comparison between an active reactor and an autoclaved control indicated that NH3 removal resulted from nitrification directly, as well as from enhanced absorption resulting from acidity produced by nitrification. Spatial distribution studies (20 ppm only) after 8 days of operation showed that nearly 95% of the NH3 could be accounted for in the lower 25% of the biofilter matrix, proximate to the port of entry. Periodic analysis of the biofilter material (20 and 50 ppm) showed accumulation of the nitrification product NO3- early in the operation, but later both NO2- and NO3- accumulated. Additionally, the N-mass balance accountability dropped from near 100% early in the experiments to approximately 95 and 75% for the 20- and 50-ppm biofilters, respectively. A partial contributing factor to this drop in mass balance accountability was the production of NO and N2O, which were detected in the biofilter exhaust.

NASA Discipline Life Support Systems↗
NASA NTRS1984

Alterations in internal partitioning of carbon in soybean plants in response to nitrogen stress

Alterations in internal partitioning of carbon were evaluated in plants exposed to limited nitrogen supply. Vegetative, nonnodulated soybean plants (Glycine max (L.) Merrill, 'Ransom') were grown for 21 days with 1.0 mM NO3- and then exposed to solutions containing 1.0, 0.1, or 0.0 mM NO3- for a 25-day treatment period. In nitrogen-limited plants, there were decreases in emergence of new leaves and in the expansion rate and final area at full expansion of individual leaves. As indicated by alterations in accumulation of dry weight, a larger proportion of available carbon in the plant was partitioned to the roots with decreased availability of nitrogen. Partitioning of reduced nitrogen to the root also was increased and, in plants devoid of an external supply, considerable redistribution of reduced nitrogen from leaves to the root occurred. The general decrease in growth potential and sink strength for nutrients in leaves of nitrogen-limited plants suggested that factors other than simply availability of nitrogen likely were involved in the restriction of growth in the leaf canopy and the associated increase in carbon allocation to the roots.

Soybeans/growth & development/metabolism↗
NASA NTRS1985

Tomato responses to ammonium and nitrate nutrition under controlled root-zone pH

Tomato (Lycopersicon esculentum L. Mill. 'Vendor') plants were grown for 21 days in flowing solution culture with N supplied as either 1.0 mM NO3- or 1.0 mM NH4+. Acidity in the solutions was automatically maintained at pH 6.0. Accumulation and distribution of dry matter and total N and net photosynthetic rate were not affected by source of N. Thus, when rhizosphere acidity was controlled at pH 6.0 during uptake, either NO3- or NH4+ can be used efficiently by tomato. Uptake of K+ and Ca2+ were not altered by N source, but uptake of Mg2+ was reduced in NH4(+)-fed plants. This indicates that uptake of Mg2+ was regulated at least partially by ionic balance within the plant.

NASA Program CELSS↗
NASA NTRS1994

Dry matter and nitrogen accumulation are not affected by superoptimal concentration of ammonium in flowing solution culture with pH control

While it is known that superoptimal concentrations of the nitrate (NO3-) ion in solution culture do not increase NO3- uptake or dry matter accumulation, the same is not known for the ammonium (NH4+) ion. An experiment was conducted utilizing flowing solution culture with pH control to investigate the influence of superoptimal NH4+ concentrations on dry matter, nitrogen (N), potassium (K), calcium (Ca), and magnesium (Mg) accumulation by nonnodulated soybean plants. Increasing the NH4+ concentration in solution from 1 to 10 mM did not affect dry matter or N accumulation. Accumulations of K, Ca, and Mg were slightly decreased with increased NH4+ concentration. The NH4+ uptake system, which is saturated at less than 1mM NH4+, is able to regulate uptake of NH4+ at concentrations as high as 10 mM.

NASA Discipline Life Support Systems↗
NASA NTRS2005

Global Impacts of Gas-Phase Chemistry-Aerosol Interactions on Direct Radiative Forcing by Anthropogenic Aerosols and Ozone

We present here a first global modeling study on the influence of gas-phase chemistry/aerosol interactions on estimates of anthropogenic forcing by tropospheric O3 and aerosols. Concentrations of gas-phase species and sulfate, nitrate, ammonium, black carbon, primary organic carbon, secondary organic carbon, sea salt, and mineral dust aerosols in the preindustrial, present-day, and year 2100 (IPCC SRES A2) atmospheres are simulated online in the Goddard Institute for Space Studies general circulation model II' (GISS GCM II'). With fully coupled chemistry and aerosols, the preindustrial, presentday, and year 2100 global burdens of tropospheric ozone are predicted to be 190, 319, and 519 Tg, respectively. The burdens of sulfate, nitrate, black carbon, and organic carbon are predicted respectively to be 0.32. 0.18, 0.01, 0.33 Tg in preindustrial time, 1.40, 0.48, 0.23, 1.60 Tg in presentday, and 1.37, 1.97, 0.54, 3.31 Tg in year 2100. Anthropogenic O3 is predicted to have a globally and annually averaged present-day forcing of +0.22 W m(sup -2) and year 2100 forcing of +0.57 W m(sup -2) at the top of the atmosphere (TOA). Net anthropogenic TOA forcing by internally mixed sulfate, nitrate, organic carbon, and black carbon aerosols is estimated to be virtually zero in the present-day and +0.34 W m(sup -2) in year 2100, whereas it is predicted to be -0.39 W m(sup -2) in present-day and -0.61 W m(sup -2) in year 2100 if the aerosols are externally mixed. Heterogeneous reactions are shown to be important in affecting anthropogenic forcing. When reactions of N2O5, NO3, NO2, and HO2 on aerosols are accounted for, TOA anthropogenic O3 forcing is less by 20-45% in present-day and by 20-32% in year 2100 at mid to high latitudes in the Northern Hemisphere, as compared with values predicted in the absence of heterogeneous gas aerosol reactions. Mineral dust uptake of HNO3 and O3 is shown to have practically no influence on anthropogenic O3 forcing. Heterogeneous reactions of N2Os, NO3, NO2, and HO2 are predicted to have noticeable impacts on anthropogenic aerosol forcing over industrialized areas, leading to 0-2 W m(sup -2) more anthropogenic aerosol cooling in present-day and 2-8 W m(sup -2) more cooling in year 2100 in these areas as compared with forcings calculated in the absence of heterogeneous reactions. Sea salt uptake of SO2 reduces the magnitude of TOA aerosol cooling by 0.5-1 W m(sup -2) over the oceans around 60 N in the present-day and year 2100 scenarios. Near dust sources, mineral dust uptake of SO2 and HNO3 leads to less anthropogenic aerosol cooling by 0.5-1 W m(sup -2) in the present day and 1-2 W m(sup -2) in year 2100.

Liao, Hong↗
NASA NTRS2017

Investigation of Global Particulate Nitrate from the AeroCom Phase III Experiment

An assessment of global particulate nitrate and ammonium aerosol based on simulations from nine models participating in the Aerosol Comparisons between Observations and Models (AeroCom) phase III study is presented. A budget analysis was conducted to understand the typical magnitude, distribution, and diversity of the aerosols and their precursors among the models. To gain confidence regarding model performance, the model results were evaluated with various observations globally, including ground station measurements over North America, Europe, and east Asia for tracer concentrations and dry and wet depositions, as well as with aircraft measurements in the Northern Hemisphere mid-to-high latitudes for tracer vertical distributions. Given the unique chemical and physical features of the nitrate occurrence, we further investigated the similarity and differentiation among the models by examining (1) the pH-dependent NH3 wet deposition; (2) the nitrate formation via heterogeneous chemistry on the surface of dust and sea salt particles or thermodynamic equilibrium calculation including dust and sea salt ions; and (3) the nitrate coarse-mode fraction (i.e., coarse/total). It is found that HNO3, which is simulated explicitly based on full O3-HOx-NOx-aerosol chemistry by all models, differs by up to a factor of 9 among the models in its global tropospheric burden. This partially contributes to a large difference in NO3(-), whose atmospheric burden differs by up to a factor of 13. The atmospheric burdens of NH3 and NHC 4 differ by 17 and 4, respectively. Analyses at the process level show that the large diversity in atmospheric burdens of NO3(-), NH3, and NHC4(+) is also related to deposition processes. Wet deposition seems to be the dominant process in determining the diversity in NH3 and NHC 4 lifetimes. It is critical to correctly account for contributions of heterogeneous chemical production of nitrate on dust and sea salt, because this process overwhelmingly controls atmospheric nitrate production (typically greater than 80 %) and determines the coarse- and fine-mode distribution of nitrate aerosol.

Ammonium aerosol based on simulations↗
NASA NTRSDate not supplied

Isotopically Tracking Nitrogen Oxides, Nitrous Acid, And Nitric Acid, Particulate Nitrate from Wildfire During FIREX-AQ

Wildfires are an important source of reactive nitrogen species including nitrogen oxides (NOx = NO + NO2) and nitrous acid (HONO), as well as products such as nitric acid (HNO3) and particulate nitrate (p-NO3-). These species have strongly influence air quality and climate. In summer of 2019 (July 25 —August 21), as part of the FIREX-AQ ground mission, we drove ~3000 miles and sampled smoke of different ages in both daytime and nighttime from 5 different wildfires in the western US. Using recently developed methods that have been validated in both laboratory and field settings, we conducted high time resolution collection of NOx, NO2, HONO, HNO3, and p-NO3- for off-line characterization of isotopic composition δ15N, δ18O and Δ17O (=δ17O−0.52 δ18O). δ15N serves as a potential tracer for tracking sources and reactive nitrogen cycling pathways, δ18O and Δ17O provide key information about oxidation pathways (i.e. O3 versus RO2). Our measured δ15N for HONO ranges from -4.9‰ to +5.2‰ and -8‰ to +5.2‰ respectively, in the majority overlapping with our prior lab controlled burning results, which suggests the capability of δ15N for tracing the biomass burning emissions against other sources including vehicular emissions and soil emissions. In addition, our measurements show δ18O and Δ17O for NO2 and HONO vary significantly day vs night, as well as in young smoke vs aged smoke, likely reflecting different oxidizing mechanisms under different smoke conditions. Preliminary results of isotopic signatures of all the above reactive nitrogen species will be presented, and their relationships will be explored to identify wildfire derived reactive nitrogen source signatures and to constrain atmospheric processing pathways (e.g. secondary formation of HONO) for different fires under various smoke conditions depending on fuel types, fire conditions and meteorological conditions.

Jiajue Chai↗