Search

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]

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]

Whole air drawn from four heights within the high elevation (3,340 m asl), deep, winter snowpack at Niwot Ridge, Colorado, were sampled into stainless steel canisters, and subsequently analyzed by gas chromatography for 51 volatile inorganic and organic gases. Two adjacent plots with similar snow cover were sampled, one over bare soil and a second one from within a snow-filled chamber where Tedlar/Teflon-film covered the ground and isolated it from the soil. This comparison allowed for studying effects from processes in the snowpack itself versus soil influences on the gas concentrations and fluxes within and through the snowpack. Samples were also collected from ambient air above the snow surface for comparison with the snowpack air. Analyzed gas species were found to exhibit three different kinds of behavior: (1) One group of gases, i.e., carbon dioxide (CO2), chloroform (CHCl3), dimethylsulfide (CH3)2S, carbondisulfide (CS2), and dichlorobromomethane (CHBrCl2), displayed higher concentrations inside the snow, indicating a formation of these species and release into the atmosphere. (2) A second group of compounds, including carbon monoxide (CO), carbonyl sulfide (COS), the hydrocarbons methane, ethane, ethyne, benzene, and the halogenated compounds methylchloride (CH3Cl), methylbromide (CH3Br), dibromomethane (CH2Br2), bromoform (CHBr3), tetrachloromethane (CCl4), CFC-11, CFC-12, HCFC-22, CFC-113, 1,2-dichloroethane, methylchloroform, HCFC-141b, and HCFC-142b, were found at lower concentrations in the snow, indicating that the snow and/or soil constitute a sink for these gases. (3) For 21 other gases absolute concentrations, respectively concentration gradients, were too low to unequivocally identify their uptake or release behavior. For gases listed in the first two groups, concentration gradients were incorporated into a snowpack gas diffusion model to derive preliminary estimates of fluxes at the snow-atmosphere interface. The snowpack gradient flux technique was found to offer a highly sensitive method for the study of these surface gas exchanges. Microbial activities below this deep, winter snowpack appear to be the driving mechanism behind these gas sources and sinks. Flux results were applied to a simple box model to assess the potential contribution of the snowpack uptake rates to atmospheric lifetimes of these species. [ABSTRACT FROM AUTHOR]

Spectroradiometers using photodiode array detectors (PDAs) are increasingly applied for airborne and ground-based atmospheric measurements of spectral actinic flux densities due to their high time resolution (less than one second). However they have limited sensitivity of ultraviolet (UV) radiation for wavelengths less than about 305 nm. This results in uncertainties of ozone photolysis frequencies derived from spectral actinic flux density measurements using PDA spectrometers. To overcome this limitation a parameterization method is introduced which extrapolates the data towards the wavelength range of limited sensitivity of the PDA spectrometers (less than about 305 nm). The parameterization is based on radiative transfer simulations and is valid for measurements in the lower troposphere. The components of the suggested parameterization are the lower threshold wavelength of the PDA spectrometer, the slant ozone column (ratio of the total ozone column and the cosine of the solar zenith angle), and the ambient temperature. Tests of the parameterization with simulated actinic flux density spectra have revealed an uncertainty of the derived ozone photolysis frequency of ±5%. Field comparisons of the parameterization results with independent measurements of the ozone photolysis frequency were within ±10% for solar zenith angles less than 70^∘. Finally the parameterization was applied to airborne measurements to emphasize the advantage of high time resolution of PDA spectrometers to study ozone photolysis frequency fields in inhomogeneous cloud condtitions. [ABSTRACT FROM AUTHOR]