Ratios of the observed concentrations of Non-Methane Hydrocarbons (NMHCs) have frequently been us... more Ratios of the observed concentrations of Non-Methane Hydrocarbons (NMHCs) have frequently been used to gain insight into the loss mechanisms of those NMHCs. By choosing NMHCs with substantially different rates of reactions with a major reaction partner such as OH, together with an estimate of the OH mean concentration, a "chemical age" may be calculated for the air mass sampled. The ratio of toluene to benzene, for example, has been frequently invoked to calculate such a "chemical age". A different NMHC ratio, resulting in a substantially different calculated "chemical age", may be taken as evidence of more than one significant loss mechanism. Examples of such substantial disagreement will be presented using NMHCs that undergo rapid reaction with Cl radicals. The reconciliation of such disagreements yields an estimate of the marine boundary layer Cl concentration. This estimate will be compared to other reported indirect estimates of maritime Cl contentrations.
Studies of decaying afterglow plasmas in helium were ined near 4 deg K by immersion in a liquid h... more Studies of decaying afterglow plasmas in helium were ined near 4 deg K by immersion in a liquid helium bath. By means of a Maser Radiometer System, the electron temperature was followed below 200 deg K. Guided microwave propagation and wave interaction techniques premit determination of election number density and collision frequencies for momentum transfer. Electron temperature decay rates of the order of 150 mu sec/p(mm Hg alpha 4.2 deg K) were found. Since thermal relaxation by elastic collisions should be some two orders of magnitude faster than this, the electrons appear to be in quasiequilibrium with a slowly decaying internal heating source. Correlation of the expected decay rates of singlet metastable helium atoms with the electron temperature decay gives good agreement with the present experiment. (auth)
ABSTRACT We present simultaneous measurements of nitrate radical (NO3) and dimethylsulfide (DMS) ... more ABSTRACT We present simultaneous measurements of nitrate radical (NO3) and dimethylsulfide (DMS) from NEAQS (New England Air Quality Study). DMS is emitted from the ocean surface as a result of phytoplankton activity, whereas NO3 is produced by reaction of ozone (O3) and nitrogen dioxide (NO2) in polluted air. Photolysis by visible light and rapid reaction with NO during daytime prevent NO3 from building to significant concentration, except at night. The rapid reaction between NO3 and DMS constitutes an important sink for the latter in the polluted marine boundary layer. We will show nocturnal profiles of both compounds as well as the anticorrelations between them. These data indicate that nighttime DMS oxidation by NO3 under polluted conditions with high NO3 concentrations in the north-east coastal region of the US and daytime oxidation by OH are comparable. We will discuss the influence of transport and mixing of fresh emissions into marine air on the observed anticorrelations based on trajectory calculations and tracer measurements to distinguish between transport effects and reactions.
During the NEAQS 2002 study, in-situ NMHC measurements were made aboard the NOAA research vessel ... more During the NEAQS 2002 study, in-situ NMHC measurements were made aboard the NOAA research vessel Ronald H. Brown by a two channel automated gas chromatograph using both flame ionization and mass-spectrometric detection techniques. Five minute average samples were cryogenically trapped each 1/2 hour and analyzed immediately for C2 through C10 alkanes, C2 through C5 alkenes, C6 through C9 aromatics, C2 through C8 aldehydes and ketones, C1 through C5 alcohols and a variety of compounds of biogenic origin including 6 monoterpenes, isoprene and its primary oxidation products methacrolein and methylvinyl ketone. The relative contributions of these classes of compounds to OH photochemistry has been determined for air masses ranging from those showing significant anthropogenic influence to clean marine air. For the most anthropogenically influenced air masses, alkenes were observed to play a dominant role whereas oxy-hydrocarbons, principally acetaldehyde, were observed to dominate under cl...
... OF THE REACTION 0+ + Oa 0 + 0 AT THERMAL ENERGY FC FEHSENFELD, PD GOLDAN, AL SCHMELTEKOPF ...... more ... OF THE REACTION 0+ + Oa 0 + 0 AT THERMAL ENERGY FC FEHSENFELD, PD GOLDAN, AL SCHMELTEKOPF ... 8. J. SAVERS and D. SMITH, Atomic Collision Processes, p. 871. ... EE FERGUSON, FC FEHSENFELD, PD GOLDEN, AL SCHMELTEKOPF and HI SCHIFF, Planet. ...
The nitrate radical, NO3, formed from reaction of NO2 with O3, and dinitrogen pentoxide, N2O5, fo... more The nitrate radical, NO3, formed from reaction of NO2 with O3, and dinitrogen pentoxide, N2O5, formed from subsequent reaction of NO3 with NO2, drive several important nocturnal chemical processes, including oxidation of VOCs (by NO3) and removal of NOx (= NO + NO2) by the heterogeneous reaction of N2O5 to form either nitric acid, HNO3, and/or aerosol nitrate. Laboratory studies have shown that uptake of N2O5 on sea salt and chloride containing aerosol produces nitryl chloride, ClNO2, which after sunrise may provide a source of Cl atoms, an important oxidant of VOCs in the marine boundary layer. We have measured NO3 and N2O5, by cavity ring-down spectroscopy, on board the NOAA research vessel Ronald H. Brown during the Texas Air Quality Study - Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS/GoMACCS) 2006. In this presentation, a few aspects of nighttime nitrogen oxide chemistry in the subtropical marine boundary layer are highlighted, including (1) NO3 and N2O5 production and loss rates including uptake on aerosol in order to estimate nighttime HNO3 production and NOx loss, and (2) the impact of NO3 and N2O5 heterogeneous uptake to produce labile halogen containing compounds at night.
All of our previously published atmospheric N2O mixing ratio data must be divided by 1.07 to corr... more All of our previously published atmospheric N2O mixing ratio data must be divided by 1.07 to correct for an error that we have recently discovered in our 1975 N2O primary standard. This problem was uncovered during intercomparison of our electron-capture, gas-chromatographic measurement technique for N2O with a newly developed infrared absorption technique (Connell et al, 1980). The salient features of this intercomparison, the subsequent recalibration of our standards for N2O, CFCl3, and CF2Cl2, and the consequences of the correction required for our N2O data are summarized here.
Samples of stratospheric air were obtained at altitudes up to about 35 km from balloon flights ca... more Samples of stratospheric air were obtained at altitudes up to about 35 km from balloon flights carried out at 4 deg S (Brazil), 78 deg S (Antarctica), and 41 deg N (two flights, Wyoming) in 1978. The samples obtained were analyzed for methane using a gas chromatograph with flame ionization detection. The two Wyoming profiles and the Antarctica profile are similar. However, the Brazil profile, which is the first low-latitude stratospheric-methane profile reported, falls off much less rapidly with altitude, even when reduced to a common tropopause reference. The use of these methane profiles to deduce OH profiles is explored.
Ratios of the observed concentrations of Non-Methane Hydrocarbons (NMHCs) have frequently been us... more Ratios of the observed concentrations of Non-Methane Hydrocarbons (NMHCs) have frequently been used to gain insight into the loss mechanisms of those NMHCs. By choosing NMHCs with substantially different rates of reactions with a major reaction partner such as OH, together with an estimate of the OH mean concentration, a "chemical age" may be calculated for the air mass sampled. The ratio of toluene to benzene, for example, has been frequently invoked to calculate such a "chemical age". A different NMHC ratio, resulting in a substantially different calculated "chemical age", may be taken as evidence of more than one significant loss mechanism. Examples of such substantial disagreement will be presented using NMHCs that undergo rapid reaction with Cl radicals. The reconciliation of such disagreements yields an estimate of the marine boundary layer Cl concentration. This estimate will be compared to other reported indirect estimates of maritime Cl contentrations.
Studies of decaying afterglow plasmas in helium were ined near 4 deg K by immersion in a liquid h... more Studies of decaying afterglow plasmas in helium were ined near 4 deg K by immersion in a liquid helium bath. By means of a Maser Radiometer System, the electron temperature was followed below 200 deg K. Guided microwave propagation and wave interaction techniques premit determination of election number density and collision frequencies for momentum transfer. Electron temperature decay rates of the order of 150 mu sec/p(mm Hg alpha 4.2 deg K) were found. Since thermal relaxation by elastic collisions should be some two orders of magnitude faster than this, the electrons appear to be in quasiequilibrium with a slowly decaying internal heating source. Correlation of the expected decay rates of singlet metastable helium atoms with the electron temperature decay gives good agreement with the present experiment. (auth)
ABSTRACT We present simultaneous measurements of nitrate radical (NO3) and dimethylsulfide (DMS) ... more ABSTRACT We present simultaneous measurements of nitrate radical (NO3) and dimethylsulfide (DMS) from NEAQS (New England Air Quality Study). DMS is emitted from the ocean surface as a result of phytoplankton activity, whereas NO3 is produced by reaction of ozone (O3) and nitrogen dioxide (NO2) in polluted air. Photolysis by visible light and rapid reaction with NO during daytime prevent NO3 from building to significant concentration, except at night. The rapid reaction between NO3 and DMS constitutes an important sink for the latter in the polluted marine boundary layer. We will show nocturnal profiles of both compounds as well as the anticorrelations between them. These data indicate that nighttime DMS oxidation by NO3 under polluted conditions with high NO3 concentrations in the north-east coastal region of the US and daytime oxidation by OH are comparable. We will discuss the influence of transport and mixing of fresh emissions into marine air on the observed anticorrelations based on trajectory calculations and tracer measurements to distinguish between transport effects and reactions.
During the NEAQS 2002 study, in-situ NMHC measurements were made aboard the NOAA research vessel ... more During the NEAQS 2002 study, in-situ NMHC measurements were made aboard the NOAA research vessel Ronald H. Brown by a two channel automated gas chromatograph using both flame ionization and mass-spectrometric detection techniques. Five minute average samples were cryogenically trapped each 1/2 hour and analyzed immediately for C2 through C10 alkanes, C2 through C5 alkenes, C6 through C9 aromatics, C2 through C8 aldehydes and ketones, C1 through C5 alcohols and a variety of compounds of biogenic origin including 6 monoterpenes, isoprene and its primary oxidation products methacrolein and methylvinyl ketone. The relative contributions of these classes of compounds to OH photochemistry has been determined for air masses ranging from those showing significant anthropogenic influence to clean marine air. For the most anthropogenically influenced air masses, alkenes were observed to play a dominant role whereas oxy-hydrocarbons, principally acetaldehyde, were observed to dominate under cl...
... OF THE REACTION 0+ + Oa 0 + 0 AT THERMAL ENERGY FC FEHSENFELD, PD GOLDAN, AL SCHMELTEKOPF ...... more ... OF THE REACTION 0+ + Oa 0 + 0 AT THERMAL ENERGY FC FEHSENFELD, PD GOLDAN, AL SCHMELTEKOPF ... 8. J. SAVERS and D. SMITH, Atomic Collision Processes, p. 871. ... EE FERGUSON, FC FEHSENFELD, PD GOLDEN, AL SCHMELTEKOPF and HI SCHIFF, Planet. ...
The nitrate radical, NO3, formed from reaction of NO2 with O3, and dinitrogen pentoxide, N2O5, fo... more The nitrate radical, NO3, formed from reaction of NO2 with O3, and dinitrogen pentoxide, N2O5, formed from subsequent reaction of NO3 with NO2, drive several important nocturnal chemical processes, including oxidation of VOCs (by NO3) and removal of NOx (= NO + NO2) by the heterogeneous reaction of N2O5 to form either nitric acid, HNO3, and/or aerosol nitrate. Laboratory studies have shown that uptake of N2O5 on sea salt and chloride containing aerosol produces nitryl chloride, ClNO2, which after sunrise may provide a source of Cl atoms, an important oxidant of VOCs in the marine boundary layer. We have measured NO3 and N2O5, by cavity ring-down spectroscopy, on board the NOAA research vessel Ronald H. Brown during the Texas Air Quality Study - Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS/GoMACCS) 2006. In this presentation, a few aspects of nighttime nitrogen oxide chemistry in the subtropical marine boundary layer are highlighted, including (1) NO3 and N2O5 production and loss rates including uptake on aerosol in order to estimate nighttime HNO3 production and NOx loss, and (2) the impact of NO3 and N2O5 heterogeneous uptake to produce labile halogen containing compounds at night.
All of our previously published atmospheric N2O mixing ratio data must be divided by 1.07 to corr... more All of our previously published atmospheric N2O mixing ratio data must be divided by 1.07 to correct for an error that we have recently discovered in our 1975 N2O primary standard. This problem was uncovered during intercomparison of our electron-capture, gas-chromatographic measurement technique for N2O with a newly developed infrared absorption technique (Connell et al, 1980). The salient features of this intercomparison, the subsequent recalibration of our standards for N2O, CFCl3, and CF2Cl2, and the consequences of the correction required for our N2O data are summarized here.
Samples of stratospheric air were obtained at altitudes up to about 35 km from balloon flights ca... more Samples of stratospheric air were obtained at altitudes up to about 35 km from balloon flights carried out at 4 deg S (Brazil), 78 deg S (Antarctica), and 41 deg N (two flights, Wyoming) in 1978. The samples obtained were analyzed for methane using a gas chromatograph with flame ionization detection. The two Wyoming profiles and the Antarctica profile are similar. However, the Brazil profile, which is the first low-latitude stratospheric-methane profile reported, falls off much less rapidly with altitude, even when reduced to a common tropopause reference. The use of these methane profiles to deduce OH profiles is explored.
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