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NASA's Student Airborne Research Program (SARP) has completed 13 years of airborne student research since its inception in 2009. The 8-week summer internship program provides students, typically rising undergraduate seniors, with an opportunity to get hands-on experience in making Earth system measurements using NASA's airborne science platforms. Students also make complementary surface-based measurements, analyze airborne and surface data in the context of related data (e.g. coincident satellite measurements or prior-year SARP data), and present results to peers, program leadership, agency management, and the community. The program splits its time between the NASA Armstrong flight facility in Palmdale, California, and the University of California, Irvine. It is implemented with participation of faculty advisors (who provide many of the instruments used) and graduate student mentors, under the overall leadership of the NASA Earth Science Division. Disciplinary foci include atmospheric gases and aerosols, ocean biology, and terrestrial ecology using both in situ and remote sensing instruments. Students are also taken on site visits to nearby laboratories and facilities and attend lectures from visiting faculty and NASA agency personnel. The program engages approximately 30 students per year, with overall approximate gender balance. The program has a high rate of STEM retention, and its alumni are actively engaged in graduate and postgraduate programs in Earth system science and other disciplines. A summary of scientific and programmatic outcomes and a description of how the program has evolved will be presented. [ABSTRACT FROM AUTHOR]

Author(s): Peter M. Edwards [1, 2, 8]; Steven S. Brown (corresponding author) [1]; James M. Roberts [1]; Ravan Ahmadov [1, 2]; Robert M. Banta [1]; Joost A. deGouw [1, 2]; [...]

Submicron aerosol was measured to the southwest of Houston, Texas, during winter and summer 2014 to investigate its seasonal variability. Data from a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) indicated that organic aerosol (OA) was the largest component of nonrefractory submicron particulate matter (NR-PM 1) (on average, 38 % ± 13 % and 47 % ± 18 % of the NR-PM 1 mass loading in winter and summer, respectively). Positive matrix factorization (PMF) analysis of the OA mass spectra demonstrated that two classes of oxygenated OA (less- and more-oxidized OOA, LO and MO) together dominated OA mass in summer (77 %) and accounted for 39 % of OA mass in winter. The fraction of LO-OOA (out of total OOA) is higher in summer (70 %) than in winter (44 %). Secondary aerosols (sulfate + nitrate + ammonium + OOA) accounted for ∼76 % and 88 % of NR-PM 1 mass in winter and summer, respectively, indicating NR-PM 1 mass was driven mostly by secondary aerosol formation regardless of the season. The mass loadings and diurnal patterns of these secondary aerosols show a clear winter–summer contrast. Organic nitrate (ON) concentrations were estimated using the NOx+ ratio method, with contributions of 31 %–66 % and 9 %–17 % to OA during winter and summer, respectively. The estimated ON in summer strongly correlated with LO-OOA (r=0.73) and was enhanced at nighttime. The relative importance of aqueous-phase chemistry and photochemistry in processing OOA was investigated by examining the relationship of aerosol liquid water content (LWC) and the sum of ozone (O3) and nitrogen dioxide (NO2) (Ox = O3+NO2) with LO-OOA and MO-OOA. The processing mechanism of LO-OOA apparently was related to relative humidity (RH). In periods of RH < 80 %, aqueous-phase chemistry likely played an important role in the formation of wintertime LO-OOA, whereas photochemistry promoted the formation of summertime LO-OOA. For periods of high RH > 80 %, these effects were opposite those of low-RH periods. Both photochemistry and aqueous-phase processing appear to facilitate increases in MO-OOA concentration except during periods of high LWC, which is likely a result of wet removal during periods of light rain or a negative impact on its formation rate. The nighttime increases in MO-OOA during winter and summer were 0.013 and 0.01 µ g MO-OOA per µ g of LWC, respectively. The increase in LO-OOA was larger than that for MO-OOA, with increase rates of 0.033 and 0.055 µ g LO-OOA per µ g of LWC at night during winter and summer, respectively. On average, the mass concentration of LO-OOA in summer was elevated by nearly 1.2 µ g m -3 for a ∼20page9642 µ g change in LWC, which was accompanied by a 40 ppb change in Ox. [ABSTRACT FROM AUTHOR]

Submicron aerosol was measured to the southwest of Houston, Texas during winter and summer 2014 to investigate its seasonal variability. Data from a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) indicated that organic aerosol (OA) was the largest component of non-refractory submicron particulate matter (NR-PM1) (on average, 46 ± 13% and 55 ± 18% of the NR-PM1 mass loading in winter and summer, respectively). Positive matrix factorization (PMF) analysis of the OA mass spectra demonstrated that two classes of oxygenated OA (less and more-oxidized OOA, LO and MO) together dominated OA mass in summer (77%) and accounted for 42% of OA mass in winter. The fraction of LO-OOA (out of total OOA) is higher in summer (69%) than in winter (44%). Secondary aerosols (sulfate + nitrate + ammonium + OOA) accounted for ~ 76% and 89% of NR-PM1 mass in winter and summer, respectively, indicating NR-PM1 mass was driven mostly by secondary aerosol formation regardless of the season. The mass loadings and diurnal patterns of these secondary aerosols show a clear winter/summer contrast. Organic nitrate (ON) concentrations were estimated using the NOx+ ratio method, with an average contribution of ~ 15% and 37% to OA during winter and summer campaign, respectively. The estimated ON in summer strongly correlated with LO-OOA (r = 0.73) and was enhanced at nighttime. The relative importance of aqueous-phase chemistry and photochemistry in processing OOA was investigated by examining the relationship of aerosol liquid water content (LWC) and the sum of ozone (O3) and nitrogen dioxide (NO2) (Ox = O3 + NO2) with LO-OOA and MO-OOA. The processing mechanism of LO-OOA apparently depended on relative humidity (RH). In periods of RH < 80%, aqueous-phase chemistry likely played an important role in the formation of wintertime LO-OOA, whereas photochemistry promoted the formation of summertime LO-OOA. For periods of high RH > 80%, these effects were opposite that of low RH periods. Both photochemistry and aqueous-phase processing appear to facilitate MO-OOA formation except during periods of high LWC, which is likely a result of wet removal during periods of light rain. The nighttime increases of MO-OOA during winter and summer were 0.013 and 0.01 μg MO-OOA per μg of LWC, respectively. The increase of LO-OOA was larger than that for MO-OOA, with increase rates of 0.033 and 0.055 μg LO-OOA per μg of LWC at night during winter and summer, respectively. On average, the mass concentration of LO-OOA in summer was elevated by nearly 1.2 μg m-3 for a ~ 20 μg change in LWC, which is accompanied by a 40 ppb change in Ox. [ABSTRACT FROM AUTHOR]

Gas-phase biogenic volatile organic compounds (BVOCs) are oxidized in the troposphere to produce secondary pollutants such as ozone (O3), organic nitrates (RONO2), and secondary organic aerosol (SOA). Two coupled zero-dimensional models have been used to investigate differences in oxidation and SOA production from isoprene and α-pinene, especially with respect to the nitrate radical (NO3), above and below a forest canopy in rural Michigan. In both modeled environments (above and below the canopy), NO3 mixing ratios are relatively small (< 0.5 pptv); however, daytime (08:00-20:00 LT) mixing ratios below the canopy are 2 to 3 times larger than those above. As a result of this difference, NO3 contributes 12 % of total daytime α-pinene oxidation below the canopy while only contributing 4 % above. Increasing background pollutant levels to simulate a more polluted suburban or peri-urban forest environment increases the average contribution of NO3to daytime below-canopy α-pinene oxidation to 32 %. Gas-phase RONO2 produced through NO3 oxidation undergoes net transport upward from the below-canopy environment during the day, and this transport contributes up to 30 % of total NO3-derived RONO2 production above the canopy in the morning (~ 07:00). Modeled SOA mass loadings above and below the canopy ultimately differ by less than 0.5 μg m-3, and extremely low-volatility organic compounds dominate SOA composition. Lower temperatures below the canopy cause increased partitioning of semi-volatile gas-phase products to the particle phase and up to 35 % larger SOA mass loadings of these products relative to above the canopy in the model. Including transport between above- and below-canopy environments increases above-canopy NO3-derived α-pinene RONO2 SOA mass by as much as 45 %, suggesting that below-canopy chemical processes substantially influence above-canopy SOA mass loadings, especially with regard to monoterpene-derived RONO2. [ABSTRACT FROM AUTHOR]

Gas-phase biogenic volatile organic compounds (BVOCs) are oxidized in the troposphere to produce secondary pollutants such as ozone (O3), organic nitrates (RONO2), and secondary organic aerosol (SOA). The nitrate radical (NO3) is especially reactive towards isoprene and monoterpenes such as α-pinene. A zero-dimensional model has been used to investigate differences in oxidation and SOA production from these two BVOCs, especially with respect to hydroxyl radical (OH) and NO3, above and below a forest canopy in rural Michigan using local data and data from a monitoring site in Detroit. In all modeled scenarios, NO3 concentrations are relatively small (0.5-3 pptv); however, daytime concentrations below the canopy are two-to-three times larger than those above. In the rural scenario, NO3 contributes up to 20% of daytime oxidation of α-pinene below the canopy, and this contribution increases to around 40% in the polluted cases. Oxidation of isoprene is almost entirely dominated by reaction with OH, as expected. The most significant first-generation RONO2 formation mechanism varies significantly between scenarios and by canopy location. Nonetheless, in every scenario, daytime production of first-generation RONO2 through NO3 + α-pinene is more significant below the canopy than above. While SOA mass loadings are moderate (2 μg m-3 or less), total SOA production is consistently enhanced below the canopy, due to the combined effects of elevated isoprene and reduced NO concentrations. Furthermore, below the canopy, the total amount of RONO2 SOA produced through NO3 oxidation of α-pinene during the daytime (10:00-18:00), while small in absolute terms, is more than twice as large as the amount produced above the canopy during that time period in every scenario. In the rural ambient case, a minimum of 74% of α-pinene RONO2 SOA is formed solely from initial oxidation by NO3. The relative abundances of HO2 and NO are shown to substantially impact both total SOA production and RONO2 SOA composition. The results presented emphasize the need for more detailed studies regarding the influence of NO3 throughout forest canopies in different environments. [ABSTRACT FROM AUTHOR]

Abstract: Concentrations of CO, SO2, NO, NO2, and NOY were measured atop the University of Houston''s Moody Tower supersite during the 2006 TexAQS-II Radical and Aerosol Measurement Project (TRAMP). The lowest concentrations of all primary and secondary species were observed in clean marine air in southerly flow. SO2 concentrations were usually low, but increased dramatically in sporadic midday plumes advected from sources in the Houston Ship Channel (HSC), located NE of the site. Concentrations of CO and NOx displayed large diurnal variations in keeping with their co-emission by mobile sources in the Houston Metropolitan Area (HMA). CO/NOx emission ratios of 5.81 ± 0.94 were observed in the morning rush hour. Nighttime concentrations of NOx (NOx = NO + NO2) and NOY (NOY = NO + NO2 + NO3 + HNO3 + HONO + 2∗N2O5 + HO2NO2 + PANs + RONO2 + p-NO3 − + …) were highest in winds from the NNW-NE due to emission from mobile sources. Median ratios of NOx/NOY were approximately 0.9 overnight, reflecting the persistence and/or generation of NOZ (NOZ = NOY − NOx) species in the nighttime Houston boundary layer, and approached unity in the morning rush hour. Daytime concentrations of NOx and NOY were highest in winds from the HSC. NOx/NOY ratios reached their minimum values (median ca 0.63) from 1300 to 1500 CST, near local solar noon, and air masses often retained enough NOx to sustain additional O3 formation farther downwind. HNO3 and PANs comprised the dominant NOZ species in the HMA, and on a median basis represented 17–20% and 12–15% of NOY, respectively, at midday. Concentrations of HNO3, PANs, and NOZ, and fractional contributions of these species to NOY, were at a maximum in NE flow, reflecting the source strength and reactivity of precursor emissions in the HSC. As a result, daytime O3 concentrations were highest in air masses with HSC influence. Overall, our findings confirm the impact of the HSC as a dominant source region within the HMA. A comparison of total NOY measurements with the sum of measured NOY species (NOYi = NOx + HNO3 + PANs + HONO + p-NO3 −) yielded excellent overall agreement during both day ([NOY](ppb) = ([NOYi](ppb)∗1.03 ± 0.16) − 0.42; r 2 = 0.9933) and night ([NOY](ppb) = ([NOYi](ppb)∗1.01 ± 0.16) + 0.18; r 2 = 0.9975). A similar comparison between NOY–NOx concentrations and the sum of NOZi (NOZi = HNO3 + PANs + HONO + p-NO3 −) yielded good overall agreement during the day ([NOZ](ppb) = ([NOZi](ppb)∗1.01 ± 0.30) + 0.044 ppb; r 2 = 0.8527) and at night ([NOZ](ppb) = ([NOZi](ppb)∗1.12 ± 0.69) + 0.16 ppb; r 2 = 0.6899). Median ratios of NOZ/NOZi were near unity during daylight hours but increased to approximately 1.2 overnight, a difference of 0.15–0.50 ppb. Differences between NOZ and NOZi rarely exceeded combined measurement uncertainties, and variations in NOZ/NOZi ratios may have resulted solely from errors in conversion efficiencies of NOY species and changes in NOY composition. However, nighttime NOZ/NOZi ratios and the magnitude of NOZ − NOZi differences were generally consistent with recent observations of ClNO2 in the nocturnal Houston boundary layer. [Copyright &y& Elsevier]

Photochemical rate constants (j values) are crucial indicators for evaluating the importance of photochemical reactions in environmental systems. While measurement of aqueous j values via chemical actinometry is relatively straightforward under most conditions, problems arise with ambient conditions below freezing, such as at very high latitudes or altitudes. To address this problem, we have developed a new method for low temperature actinometry using solutions of acetonitrile (ACN) and water, which have freezing points down to . In this method we measure the formation of phenol from the photolysis of an-generating chromophore in the presence of benzene. Using results from laboratory tests we correct our phenol field results in to rate constants for chromophore photolysis expected for water–ice (i.e., in the quasi-liquid layer of snow grains) under the same conditions. In part 1 of this study, we use this method at Summit, Greenland on the surface snow and to depths of using hydrogen peroxide (HOOH) and nitrite as the chromophores. While the method works well for determining the rate constant for HOOH photolysis (j(HOOH)), we encountered problems using the technique with nitrite. However, measured PhOH formation rate constants for nitrite in acetonitrile, , still provide an excellent means for calculating snowpack-folding depths for photolysis (i.e., the depth over which the rate constant decreases by a factor of ). Values of j(HOOH) and determined from measurements of actinic flux (above the snow) and irradiance (in snow) suggest that the value of j(HOOH) on the surface snow at midday was in mid-March and increased by 300% by the start of May, while midday surface values were consistently throughout the season. Within the snowpack, average-folding depths determined from chemical actinometry were for j(HOOH) and for ;-folding depths determined from in-snow spectral radiometer measurements of irradiance were similar. The larger-folding depth for nitrite is because this chromophore absorbs at longer wavelengths where there is less light extinction in the snow. [Copyright &y& Elsevier]

Simultaneous high-time-resolution measurements of atmospheric NH3, HNO3, soluble gas-phase chloride, and aerosol species were made in Houston, TX, from August 5, 2010 to August 9, 2010. Gaseous NH3 was measured using a 10.4-μm external cavity quantum cascade laser-based sensor employing conventional photo-acoustic spectroscopy, while gaseous HNO3 and HCl were sampled using a mist chamber–ion chromatograph (IC) system. Particle chemical composition was determined using a particle-into-liquid-sampler–IC system. There was a large amount of variability in the gas phase mixing ratios of NH3 (3.0 ± 2.5 ppb), HNO3 (287.4 ± 291.6 ppt), and HCl (221.3 ± 260.7 ppt). Elevated NH3 levels occurred around mid-day when (0.5 ± 1.0 μg m−3) and (4.5 ± 4.3 μg m−3) also increased considerably, indicating that NH3 likely influenced aerosol particle mass. By contrast, the formation of NH4NO3 and NH4Cl was not observed during the measurements. Point sources (e.g., power plant and chemical plant) might be potential contributors to the enhancements in NH3 at the measurement site under favorable meteorological conditions. Increased particle number concentrations were predicted by the SAM-TOMAS model downwind of a large coal-fired power plant when NH3 emissions (based on these measurements) were included, highlighting the potential importance of NH3 with respect to particle number concentration. Separate measurements also indicate the role of NH3 in new particle formation in Houston under low-sulfur conditions. [ABSTRACT FROM AUTHOR]

Abstract: Nitrous acid (HONO), nitric acid (HNO3), and organic aerosol were measured simultaneously atop an 18-story tower in Houston, TX during August and September of 2006. HONO and HNO3 were measured using a mist chamber/ion chromatographic technique, and aerosol size and chemical composition were determined using an Aerodyne quadrupole aerosol mass spectrometer. Observations indicate the potential for a new HONO formation pathway: heterogeneous conversion of HNO3 on the surface of primary organic aerosol (POA). Significant HONO production was observed, with an average of 0.97ppbvevent−1 and a maximum increase of 2.2ppb in 4h. Nine identified events showed clear HNO3 depletion and well-correlated increases in both HONO concentration and POA-dominated aerosol surface area (SA). Linear regression analysis results in correlation coefficients (r 2) of 0.82 for HONO/SA and 0.92 for HONO/HNO3. After correction for established HONO formation pathways, molar increases in excess HONO (HONOexcess) and decreases in HNO3 were nearly balanced, with an average HONOexcess/HNO3 value of 0.97. Deviations from this mole balance indicate that the residual HNO3 formed aerosol-phase nitrate. Aerosol mass spectral analysis suggests that the composition of POA could influence HONO production. Several previously identified aerosol-phase PAH compounds were enriched during events, suggesting their potential importance for heterogeneous HONO formation. [Copyright &y& Elsevier]

We present data collected from a number of snow-covered environments including two polar locations (Summit, Greenland and the South Pole) and two mid-latitude regions (a remote site in northern Michigan, and Niwot Ridge, Colorado). At each site, concentrations of and were enhanced within the interstitial air near the snow surface, compared to levels in boundary layer air. Fluxes of from surface snow to the atmosphere were observed at each site except Niwot Ridge, where appeared to have a sink. The mid-latitude sites showed significant emissions of , mostly originating at the ground surface and traveling up through the snow, while at the polar locations emissions from firn air were relatively small. In general, methyl halide mixing ratios in firn air were significantly greater at Summit than at the South Pole, with Summit showing a strong diurnal cycle in the production of alkyl halides that was well correlated with actinic radiation and firn temperature. We suggest that the most likely route to alkyl halide formation is through an acid catalyzed nucleophilic substitution of an alcohol type function by a halide, both of which should be preferentially segregated to the quasi-liquid layer at the surface of the snow grains. A series of experiments using a snow-filled quartz chamber irradiated by natural sunlight allowed estimation of emission trends that were hard to measure in the natural snowpack. These static chamber experiments confirmed significant production of the primary alkyl halides, following the order . Our observations at all four locations, including polar and mid-latitude sites, imply that alkyl halide production may be associated with all surface snows. [Copyright &y& Elsevier]