A43A-0865
The Day-to-day Variability of Mesospheric Water Vapor at High Latitude - a Comparison Between Microwave Observations and Calculations by Means of the GCM LIMA
Water vapor measurements in the mesosphere employing the microwave technique were carried out in high latitudes at ALOMAR (69.29 N, 16.03 E), Norway. The observed water vapor mixing ratios are marked by pronounced variations with planetary time scale. As the chemical lifetime of water vapor is very large in the mesosphere the variations reflect transport processes triggered by the planetary wave activity. A prominent signature is the quasi 5-day wave, actually having a period varying around this value. Using our real-date GCM LIMA (Leibniz-Institute Middle Atmosphere model) of the Leibniz-Institute of Atmospheric Physics in Kühlungsborn, Germany, the model output satisfactory reproduces the measured variations although in detail various differences occur between observations and calculations. In particular, the annual variation including intra-annual variations as caused by sudden stratospheric warmings is mirrored by the model. We discuss the results for different years in terms of dynamics and chemistry.
A43A-0866
A New Water Vapor Dataset From The Tropics To The Arctic Obtained By The Airborne Microwave Radiometer AMSOS
Water vapor plays a key role in the earth atmosphere. Due to strong absorption of radiation it contributes significantly to the greenhouse effect and to changes in climate. Additionally it is involved in processes related to ozone depletion in the middle atmosphere. Further it is an excellent tracer for studies of atmospheric motion due to its long chemical lifetime. Data sets of water vapor can thus help to understand important atmospheric processes. With the Airborne Microwave Stratospheric Observing System (AMSOS), a microwave radiometer carried by a Learjet of the Swiss Airforce, we measured the latitudinal distribution of water vapor from the tropics to the north pole during one week per year from 1998 to 2006. The instrument was flown in spring or autumn during active stratospheric periods. Measurements inside the polar vortex as well as in the tropics including one overflight of the equator were accomplished. We present the water vapour dataset obtained by the AMSOS instrument. Vertical profiles are retrived from spectra by an optimal estimation method. The vertical range extends from the upper troposphere to the mesosphere. The width of the averaging kernels is between 8 and 16 km. The horizontal resolution is about 57 km. The obtained profiles show clearly the water vapour minimum and maximum in the stratosphere, an elevated hygropause in the tropics in contrast to the poles, and dehydration in the polar upper stratosphere in early spring related to sinking of air masses inside the polar vortex. Data are validated against a set of instruments comprising satellite, ground-based, airborne remote sensing and in-situ instruments.
A43A-0867
Mesospheric CO Intrusion in the Arctic Stratosphere
Unusually high amounts of CO (up to 450ppb) have been measured in the Arctic winter stratosphere during balloon flights of the JPL MkIV interferometer. High altitude CO is mainly produced from the photolysis of carbon dioxide in the lower thermosphere. It then follows the meridional circulation towards the winter hemisphere polar night region, where it accumulates and descends into the middle atmosphere. The photochemical lifetime of CO makes it an important indicator of vertical transport in the mesosphere. These measurements give further evidence of significant amounts of mesospheric air descending down to as low as 25-30km in the Arctic Polar vortex, which is not a well-observed phenomenon. Mesospheric air is also enhanced in reactive nitrogen compounds which can affect ozone. The ability of the MkIV instrument to simultaneously measure more than 30 different gases allows us to better quantify the impact of this phenomenon on the chemical composition of the polar stratosphere.
A43A-0868
Mesospheric HCN, N2O, and CO: Measurements and Implications for Dynamics and Chemistry
We present contemporaneous, colocated, ground-based observations of N2O (upper stratosphere), HCN (lower mesosphere), and CO (upper mesosphere). Of these, 50-70 km HCN data are unique, and of interest for understanding lower mesospheric chemistry. Reaction with OH is a primary sink for HCN, suggesting HCN abundances may be useful in studies of lower mesospheric hydrogen (HOx) chemistry. Measured increases with altitude of both HCN [Jaramillo et al., 1988] and CH3CN [Livesey et al., 2001; 2004] in the stratosphere are not understood, in that neither has a known stratospheric source. Chemical conversion of HCN to/from CH3CN is not supported by model studies [Brasseur et al., 1985], but the CN bond in each molecule suggests that studying the chemistry of one will shed light on the other. Global measurements of stratospheric N2O and upper mesospheric CO have been used in many previous studies as indicators of large scale atmospheric transport, N2O moving upward from the troposphere, and CO downward from the thermosphere. HCN is analogous to N2O, in that each is produced in the troposphere, then transported upward as (nearly) inert species, until reaching an altitude where photochemical destruction begins. Because HCN persists to higher altitudes than does N2O, it is a candidate for studies of large scale lower mesospheric transport, analogous to N2O in studies of the statosphere. We compare local N2O, HCN, and CO abundances for what they may indicate about bulk transport across the full altitude range 40-100 km, and discuss HCN as a candidate for future global studies of lower mesospheric transport. Ground-based observations of the 266 GHz HCN, 226 GHz N2O, and 230 GHz CO lines were made over the period 1998-2002, using the 12-meter telescope at Kitt Peak AZ [a facility of NSF, operated by the Univ. of Arizona Steward Observatory, under loan agreement with NRAO]. These are passive observations of rotational LTE emission lines. Frequency switching is used to remove the lower atmospheric background, and altitudes of the measured species are derived from shape of each pressure broadened line.
A43A-0869
Enhanced capabilities for Aura MLS, OMI and HIRDLS data within Giovanni
The NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) has developed an on-line web based data visualization and analysis system known as Giovanni for accessing EOS Aura satellite data. Aura was launched in July 2004 with four instruments designed to measure atmospheric trace gases, aerosols, and clouds. The four instruments include the Microwave Limb Sounder (MLS), the Ozone Monitoring Instrument (OMI), the High Resolution Dynamics Limb Sounder (HIRDLS), and the Tropospheric Emission Spectrometer (TES). Currently, Giovanni provides easy access to data from the Aura MLS, OMI and HIRDLS instruments. Users can access ozone, NO2, SO2, aerosol, cloud, UVB surface irradiance, BrO, HCHO and OCLO data from the OMI instrument. Visualization services include 2-D maps, animated maps, time series with statistics, scatter plots, as well as latitude vs. time and longitude vs. time Hovmoller plots. New capabilities to display correlation maps, anomaly plots will be added to Giovanni. MLS vertical profiles of ozone, water vapor, temperature, BrO, ClO, CO, HCl, HCN, HNO3, HO2, HOCl, N2O, OH, along with cloud ice water content, relative humidity with respect to ice, and geopotential height are available to users. Zonal mean and global gridding services will be added to Giovanni for MLS data. HIRDLS vertical profiles of ozone, temperature, and HNO3 have also been recently added to Giovanni. Other parameters and services will be added as they become available. In the future, TES vertical profile data will be made available through Giovanni. http://giovanni.gsfc.nasa.gov
A43A-0870
The Ozone Hole -- a Mystery Reborn?
In 1985, Farman et al. discovered the near complete disappearance of the stratospheric ozone layer over Antarctica in spring. This 'Ozone Hole' took the atmospheric research community by surprise as it could not be explained by the known catalytic cycles removing ozone in the stratosphere. McElroy et al. (1986) and Molina and Molina (1987) seemed to have solved the enigma by proposing two new catalytic cycles -- the ClO-BrO-cycle and the ClO dimer cycle -- that could rapidly destroy ozone at cold temperatures and high zenith angles. Subsequent work describing the kinetics of these cycles as well as stratospheric observations of chlorine and bromine compounds supported their theory and led to atmospheric chemistry models reproducing observed ozone loss reasonably well. Today, more than 20 years after the discovery of the ozone hole and the ratification of the Montreal Protocol, a new laboratory study (Pope et al., 2007) -- suggesting much smaller absorption cross sections and hence photolysis rates of the ClO dimer -- seriously calls into question our understanding of how ozone is destroyed in the spring polar stratosphere. With the new cross sections, both the dimer cycle and the ClO-BrO-cycle run much slower, and observations of neither chlorine compounds nor ozone loss are reproduced by model simulations (von Hobe et al., 2007): the known catalytic cycles cannot cause an ozone hole. Obviously, this also calls into question our ability to predict future polar ozone depletion. In search for an explanation, we discuss possible shortcomings of the Pope et al. experiment that could lead to an underestimation of the dimer absorption and examine various new chemical processes for their likelihood to influence chlorine partitioning and cause significant ozone loss in the atmosphere and at the same time go undetected in laboratory based kinetic studies. A strategy is presented for designing the tests needed to unambiguously confirm or rule out proposed solutions to the dilemma. Farman, J.C. et al., Nature 315, 207, 1985. McElroy, M.B. et al., Nature 321, 759, 1986. Molina, L.T. and Molina, M.J., J. Phys. Chem. 91, 433, 1987. Pope, F.D.et al., J. Phys. Chem. A 111, 4322, 2007. von Hobe, M. et al., Atmos. Chem. Phys. 7, 3055, 2007.
A43A-0871
Impact of Recent Laboratory Measurements of the ClOOCl Absorption Cross Section On Our Understanding of Polar Ozone Chemistry
The photolysis of ClOOCl is crucial in determining the rate of polar ozone loss due to the ClO+ClO cycle. New laboratory measurements of the ClOOCl cross section suggest that its photolysis is about a factor of six slower than a value based on current recommendations. We show the incorporation of these new cross sections into a photochemical model leads to poor agreement with values of ClO and ClOOCl measured during the SOLVE and VINTERSOL campaigns. For both campaigns the model under-estimates measured ClO and over-estimates measured ClOOCl by amounts that are much larger than the measurement uncertainties. We also examine implications of the new ClOOCl cross section measurement on the chlorine budget, using observations of ClO and HCl from Aura MLS and ClNO3 from ACE. These comparisons indicate that a model using the new cross section, and no other changes, provides a poor description of the chlorine photochemistry. Such a simulation also results in much slower ozone loss rates compared to a model using standard chemistry. We use the various data sets to test a variety of processes that could be invoked to resolve these discrepancies. Implications of proposed new chemical mechanisms for ozone loss rates are also discussed.
A43A-0872
MLS measurements of polar BrO
We discuss measurements of stratospheric BrO obtained by the Microwave Limb Sounder (MLS) on the Aura satellite. These measurements span an altitude range of 32 to 42 km. Previous validation of MLS BrO in the mid- latitudes and tropics took advantage of the diurnal variation of BrO at those latitudes to remove large biases in the data. For winter and summer polar BrO, we cannot remove biases that way. Therefore we use a different method, estimating the biases from non-polar regions, as well as from polar regions in the spring and fall, when polar BrO undergoes a diurnal variation. We then subtract these estimates from the MLS BrO data. To compare polar MLS BrO measurements with lower-altitude measurements obtained by the balloon-borne instruments DOAS, SAOZ-BrO, and SLS, we use a photochemical model to infer total inorganic bromine (Bry). Since Bry, unlike BrO, should remain approximately constant with altitude, it provides a proxy for comparison.
A43A-0873
Temperature Dependence of the Isotopic Composition of Ozone
The overall magnitude of the isotopic composition of stratosphere ozone is ~100 per mil, which is large compared with that commonly known in atmospheric chemistry and geochemistry. Using the one- and two- dimensional CalTech/JPL KINETICS models of the middle atmosphere, which include both formation and photolysis processes of ozone, we found that the calculated δ49-O3 and δ50-O3 are about 10~15 per mil larger than the measurements (Krankowsky et al. 2007). We propose that the ~10 per mil differences between the model and observations may be caused by the temperature variations. Our model shows that a reduction of ~20K in the reference temperature profile could adequately reproduce the observations. By incorporating NCEP daily temperature into our models, better agreement between model and measurements is achieved. We attribute the residuals to a possible diurnal variation in temperature. Sensitivity studies have been carried out to explore the temperature dependence of the isotopic composition of ozone in the stratosphere.
A43A-0874
Possible Excited NO2 Chemistry Has Potential to Increase Tropospheric Ozone Production Rates and Stratospheric NOX/NOY Ratio
Possible reaction of electronically excited NO2 (A, 2B1,2B2) with O2, ~~~~NO2 (A, 2B1,2B2) + O2 ~→ ~ NO + O3 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (R1) has ~ potential to increase ~ the ~ probability ~ of ~ NO2 reverting to NO while producing O3 and reduce the probability of being lost to the HNO3 reservoir. This would increase tropospheric O3 production efficiency and the stratospheric NOX/NOY ratio. It is important to investigate this matter, since air pollution affects climate mostly through the radiative forcing of O3. ~~~~~The reaction NO2~+~O2 ~ → NO~+~O3 ~ is expected to occur with a rate coefficient of 5x10-12 exp(-50,550/RT) cm3 s-1, assuming reversibility of reaction holds for the well known reaction NO~+~O3 ~ → ~ NO2~+~O2 that occurs with a rate coefficient of 3x10-12 exp(-3,000/RT) cm3 s-1. In the atmosphere in local thermodynamic equilibrium (LTE), therefore, reaction of NO2 (X 2A1) with O2 would be totally insignificant. However, due to the presence of solar photons the atmosphere is not in LTE. Excited NO2 having internal electronic energy in excess of the 50.6 kcal mole-1 activation energy (due, for example, to the absorption of solar photons) could significantly react with O2, especially if it is in the non-dissociative state. The NO2(A, 2B1, 2B2) produced by NO2 (X 2A1) + hν (≤ 500 nm) can therefore drive the reaction (R1). Note that in reaction (R1) the excitation energy is in the reactant that transfers the O atom. Thus, the reaction is more likely than not. ~~~~Data on the quenching of NO2 fluorescence by N2 and O2 [ Myer ~et~ al., J. ~ Chem.~ Phys., 44, 718, 1966] provide some support for the reaction (R1). In Myer ~et ~ al. experiment fluorescence from electronically excited NO2(A, 2B1, 2B2) was produced by the absorption of λ = 435.8 nm photons by NO2 (X 2A1). The N2 and O2 molecules quenched this fluorescence with rate constant of, respectively, 3.1 x 10-11 cm3 s-1 and 3.4 x 10-11 cm3 s-1. The quenching rate coefficient increases with the molecular complexity of the quencher (such as H2O a polar molecule with many degrees of freedom). However, the more efficient quenching by O2 relative to N2 (which are of comparable complexity) suggests a reactive channel in the case of O2. What fraction of the quenching by O2 is reactive cannot be deduced from the quenching data. However, the previous paragraph supports the conjecture k1 = 5.0 x 10-12 cm3 s-1. Assuming that the conjecture holds for excited NO2 produced by photons 400 ≤ λ ≤ 500 nm, the probability of the reaction (R1) is seen to be about 10% of the photodissociation. Details will be given in the presentation at the meeting. In summary, inclusion of the reaction pair (R1) could increase the O3 production efficiency and rate by about 10%.
A43A-0875
CF3CF=CH2 and CF3CF=CHF: Temperature Dependent OH Rate Coefficients and Global Warming Potentials
Rate coefficients, k(T), over the temperature range 206-380 K are reported for the gas phase reaction of OH radicals with 2,3,3,3-tetrafluoropropene (CF3CF=CH2) and 1,2,3,3,3-pentafluoropropene (CF3CF=CHF), which are major components in proposed substitutes for HFC134a (CF3CFH2) in mobile air conditioning units. Rate coefficients were measured under pseudo-first-order conditions in OH using pulsed laser photolysis to produce OH and laser induced fluorescence to detect it. For CF3CF=CH2, the rate coefficients are given by the Arrhenius expression k1(T) = (1.26 ± 0.11) × 10-12 exp[( 35 ± 10)/T] cm3 molecule-1 s-1 where k1(296 K) = (1.12 ± 0.09) × 10-12 cm3 molecule-1 s-1. For CF3CF=CHF, the rate coefficients are given by the non-Arrhenius expression k2(T) = (1.6 ± 0.2) × 10-18 T2 exp[(655 ± 50)/T] cm3 molecule-1 s-1 where k2(296 K) = (1.29 ± 0.06) × 10-12 cm3 molecule-1 s-1. The global warming potentials for CF3CF=CH2 and CF3CF=CHF were calculated to be <4.4 and <3.6, respectively, for the 100 year time horizon using infrared absorption cross sections measured in this work and atmospheric lifetimes of 11.9 and 10.0 days, based solely on OH reactive loss.
A43A-0876
Estimation of the OH column abundance in the lower atmosphere from space- and ground- based measurements.
OH measurements by Microwave Limb Sounder (MLS) onboard Aura during 2004 - 2007 are compared with ground-based OH column measurements by Fourier Transform Ultraviolet Spectrometer (FTUVS) over Jet Propulsion Laboratory (JPL)'s Table Mountain Facility (TMF). This is the first comparison of OH measurements from space- and ground-based instruments over seasonal and interannual time scales. The FTUVS measures the OH column abundance from the surface to the top of the atmosphere while MLS measures the OH vertical profile from 21.5 hPa through the mesosphere. MLS OH densities over TMF are integrated vertically to derive partial OH columns for comparison with TMF OH columns. The direct comparison of TMF and MLS columns thus provides an opportunity to study the seasonal variation of the residual OH in troposphere and lower stratosphere. The results are compared with GEOS-Chem OH products below 21.5 hPa, corrected for diurnal variation at Aura overpass times. Balloon and aircraft observations as well as the JPL 1-D photochemical model are employed to estimate the uncertainties in the extrapolated GEOS-Chem partial OH column. The residual OH estimated with GEOS-Chem is also added to the MLS partial OH column to generate a combined total OH column to compare with the TMF total OH column. The results generally agree, especially during summer and early fall when OH levels are high. In winter and early spring with low OH, the former is generally higher than the latter. The correlation of these two groups of data is studied based on least-square linear fits, seasonal T-tests, and contour mapping of the orthogonal chi square. Possible causes of the observed differences will be discussed.
A43A-0877
Observations and Modelling of Aircraft HOx Measurements Over West Africa
As the primary oxidant in the troposphere, the hydroxyl (OH) radical controls the processing of anthropogenic and biogenic emissions. Methane is the most abundant trace gas in the atmosphere, with ~80% of global methane being removed in tropical regions by reaction with OH. However, to date, measurements of OH in the tropical boundary layer and free troposphere have been sparse. Due to the fast intercoversion of OH and HO2, the simultaneous measurement of both species is desirable. In support of the African Monsoon Multidisciplinary Analyses (AMMA) mission occurring in West Africa, the UK FAAM (Facility for Airborne Atmospheric Measurements) BAe-146 aircraft was deployed to Niger during the summer of 2006. Alongside other observations, the first measurements of OH and HO2 in this understudied, but very important, region were made using an airborne Fluorescence Assay by Gas Expansion (FAGE) instrument. At an altitude of 1100 m and for a signal-to-noise ratio of 1, the average limit of detection for OH and HO2 were 7.2 × 105 molecule cm-3 (30 s integration time) and 3.1 × 106 molecule cm-3 (1 s integration time) respectively. OH was measured on 7 flights and HO2 on 13 flights, with a large range of air mass types encountered. Observations of OH and HO2 show great variability. A series of day and night flights on one day show HO2 concentrations varying from a maximum of 8 × 108 molecule cm- 3 at solar noon to a minimum of 1 × 107 molecule cm-3 at night. The distribution of OH over West Africa is discussed in terms of its spatial and temporal variation, with emphasis given to the differences in concentrations observed in monsoonal, Saharan and anthropogenic air. Box model calculations constrained by observations are used to investigate the mechanisms controlling the HOx concentrations. These calculations suggest that much of the variability observed in OH and HO2 can be attributed to the large variations in J(O1D), O3 and H2O observed. However, in biogenically perturbed forested regions north of the Gulf of Guinea, isoprene plays a significant role in controlling the HOx concentrations observed.
A43A-0878
OH Background Measurements and Their Significance
The hydroxyl radical, OH is known to be the primary gas phase oxidant in most tropospheric environments, however other species can contribute to the total overall oxidizing capacity. Our CIMS technique for the measurement of OH involves both a signal and a background measurement. The signal measurement is a measure of all species that react with SO2 to produce H2SO4 (which presumably is mainly OH), while the background accounts for all species that can convert SO2 into H2SO4, yet do not react with propane. This background measurement while necessary for the determination of OH, is also a measure of other strong oxidants and can be quite large even in the absence of OH (as determined via the CIMS technique). Here we will focus on OH background data obtained in marine, urban, and remote continental conditions. Correlation of these measurements with other species such as NO and SO2 will be presented. Atmospheric implications will also be discussed.
A43A-0879
Ambient air measurements of monoterpenes, oxygenated terpenes, and sesquiterpenes
Chemical ozone loss within the forest canopy and the presence of biogenic VOC (BVOC) oxidation products in and above the canopy indirectly suggest the presence of very reactive BVOCs at Blodgett Forest. As a part of the 2007 BEARPEX campaign at this coniferous forest in the Sierra Nevada Mountains of California (1300 m elevation, 38.90° N, 120.63° W,), we quantified ambient concentrations of terpenes using a modified in-situ gas chromatograph with a mass spectrometer and a flame ionization detector (GC-MS-FID). The range of terpenes observed in ambient air matched enclosure based measurements of branch level emissions. To our knowledge, these observations represent the first quantification of the oxygenated monoterpene methyl chavicol and various sesquiterpenes in ambient air. Details of the instrument modifications, diurnal profiles of the terpenes, and comparison to branch level emissions will be presented.
A43A-0880
VOC Emissions From Decomposing Leaf Litter
The emission of VOCs from the biosphere has a profound effect on the oxidative capacity of the troposphere. Most studies of the flux of reactive carbon from the biosphere have focused on BVOC emissions at leaf and canopy scales with relatively few studies investigating BVOC emissions from soils. Here we present results describing the emissions of a suite of BVOCs from different litter types under different levels of nitrogen availability. To investigate these effects, three biochemically distinct litter types (Deschampsia sp., Acomostylis sp., and Rhododendron sp.) were coarsely ground and incubated in the dark for two months under different nitrogen regimes at optimal conditions for microbial activity. We used proton transfer reaction mass spectrometry and an infrared gas analyzer (IRGA) to monitor BVOC emissions and CO2 production rates throughout the course of the investigation. When different leaf litter types decomposed, they released distinctly different types and quantities of VOCs. However, varying nitrogen availability caused the VOC signature from some litters to change dramatically. We suggest that decomposition of leaf litter could provide a substantive source of reactive carbon to the atmosphere at local and regional scales and hypothesize that nitrogen deposition may play a role in attenuating the release of some reactive species.
A43A-0881
Experimental Studies of the Kinetics of the OH-initiated Oxidation of Hydroxyacetone
Hydroxyacetone is mainly produced in the atmosphere from the reaction of the OH radical with methacrolein, which is a major product of photooxidation of isoprene. Given the abundance of isoprene throughout the troposphere, a detailed understanding of the chemistry of hydroxyacetone is required in order to fully assess the contribution of isoprene oxidation to atmospheric chemistry. Although the room temperature rate coefficient of the reaction of hydroxyacetone with OH has been investigated by several groups, there have been few measurements of the temperature dependence for this reaction. We studied the temperature dependence of the rate constant for the hydroxyacetone + OH reaction at 5 torr and between 273 and 355 K using a discharge-flow system coupled with resonance fluorescence (RF) detection of OH. Our results show that the reaction displays positive temperature dependence in contrast to recent measurements at higher pressures. The observed temperature dependence is consistent with a hydrogen abstraction reaction that proceeds through a hydrogen-bonded pre-reactive complex, similar to the OH + acetone reaction.
A43A-0882
Source of D-enriched hydrogen molecule in urban areas: photochemical decomposition of anthropogenic NMHCs?
We determined temporal variations in both the mixing ratio and δD value of atmospheric H2 in Sapporo, Japan, for every 1 hour in summer using a new CF-IRMS system that separates H2 from air with automatic multistep gas chromatograph followed by introduction to a mass spectrometer in a continuous flow of helium. The analytical precisions to determine mixing ratio and δD were ± 5 % and ± 3.6 permil, respectively. By using the correlation between δD values and reciprocal of mixing ratios, we clarified at least two major sources of H2 within the urban area. While more than 70 % of data can be explained by a simple mixing between H2 that had been derived from fossil fuel combustion (δD = -425 ± 80 permil VSMOW) and that in back ground air (δD = +120 ± 20 permil VSMOW), we have to assume additional source that has an isotopic signature around +195 ± 130 permil VSMOW to explain the other ca. 25 % data, most of which have lower H2 mixing ratios around 520 ppbv. Previous studies on δD values of urban H2 had been explained by a simple mixing between H2 in background air and that from fossil fuel combustion. Besides to fossil fuel combustion, however, photochemical decomposition of anthropogenic NMHCs could be the local source of urban H2 as well. While δD values of H2 produced through photochemical decomposition of NMHCs are not defined as yet, the D-enriched value around +190 permil VSMOW can be anticipated from past observations. We conclude that photochemical decomposition of NMHCs could be additional source of H2 in urban area at least in Sapporo. The local source strength of H2 produced through the photochemical decomposition of NMHCs can be estimated to be approximately 10 % of that from the fossil fuel combustion.
A43A-0883
Laboratory Studies of Heterogeneous Reactions of HO2 Radical with Inorganic Aerosol Particles under the Ambient Conditions
The HO2 uptake coefficient for aerosol particles ((NH4)2SO4 and NaCl) under ambient conditions (760Torr and 296K) was measured using an aerosol flow tube(AFT) coupled with a chemical conversion/laser-induced fluorescence(CC/LIF) technique. The CC/LIF technique enabled experiments to be performed at almost the same HO2 radical concentration as that in the atmosphere(~108 molecules cm-3). HO2 radicals were injected into the AFT through a vertically movable Pyrex tube. Injector position dependent profiles of LIF intensity were measured as a function of aerosol concentration at various relative humilities(RH). The uptake coefficients of dry aerosol (NaCl and (NH4)2SO4) particles were < 0.05, while the uptake coefficients of wet particles of NaCl and (NH4)2SO4 were estimated to be 0.10 and 0.15, respectively, which suggested that heterogeneous loss was enhanced by the particle containing water. To estimate the contribution of heterogeneous loss of HO2 by aerosol, the diurnal variation of HO2 using a box-model calculation was demonstrated. As a result, the daytime maximum concentrations of HO2 were changed to 95 and 70 %, relative to an absence of heterogeneous loss for marine and urban areas, respectively.
A43A-0884
Tracking the Chemical Evolution of Oxidized Organic Aerosol: Results from Aerosol Mass Spectrometer Analyses of Aged Diesel Emissions
Regional chemical transport models predicated on laboratory yield curves significantly underpredict the secondary organic aerosol (SOA) production in an aging urban air mass. The high-flux, volatile organic compounds included in these models cannot account for the large quantities of organic material that condense downwind of anthropogenic sources. Furthermore, the mass spectra of laboratory-generated SOA from these traditional high-volatility precursors do not agree with those observed in aged ambient air masses. From these observations, it is clear that atmospheric abundance is not the sole criterion for identifying SOA precursors. We have proposed that precursor vapor pressure also plays an important role, hypothesizing that SOA can form from the atmospheric oxidation of a large suite of compounds of varying vapor pressures. Here, we support this hypothesis by using an Aerosol Mass Spectrometer to track the chemical evolution of diesel exhaust as it is photochemically oxidized in an environmental chamber. Upon exposure to atmospheric oxidants, gas-phase compounds emitted from a diesel generator react to form substantial amounts of SOA. This chemistry is corroborated by changes in the mass spectrum of the organic aerosol with increasing oxidant exposure time. Explicit knowledge of the condensed-phase mass spectrum of the primary emissions from our generator allows us to decompose each mass spectrum recorded throughout the experiment into primary and residual, secondary spectra. Our analysis reveals that the chemical composition of the residual spectrum, and thus the SOA formed in these experiments, is not constant in time, but that the condensing organic material becomes increasingly oxidized over the course of an experiment. This conclusion is supported by mathematical deconvolutions of the laboratory spectra using both principal component analysis and positive matrix factorization. After several hours of aging, the total mass spectrum of the chamber aerosol closely resembles that of ambient aged organic particulate matter. This observation is consistent with our hypothesis that the species in an air mass that are responsible for SOA formation change with time. The precursors of early-forming SOA give rise to condensable products that are considerably less oxidized than those which contribute to the later SOA that forms after several generations of gas-phase oxidation. We attribute this SOA formation pattern to the presence of relatively reduced, but low vapor- pressure species that, upon oxidation, produce SOA with high yields. These species can efficiently contribute to rapid, early SOA formation, suggesting that large, saturated semi-volatile species with low vapor pressures may contribute significantly to ambient SOA concentrations.
A43A-0885
Impact of Urban Pollution on the Composition of Atmospheric Particles in Natural Environments
To gain a better understanding of the influence anthropogenic atmospheric particles have on natural environments of Puerto Rico, samples of urban, marine, and forest aerosols were collected during June-August 2007. Analyses were performed to study the carbonaceous and nitrogenous fraction of the aerosol as well as to characterize the biogenic particles of the collected samples. During this time, air masses of different origins reached the island. Preliminary results showed an average of total carbon (TC) concentrations of 0.50 micrograms of carbon per m3 for the urban site, 0.075ug/m3 for the marine site and 0.15 ug/m3 for the forest site. EC was found only in the urban site. The results obtained are highly influenced by the origin of the air masses sampled. Additional analyses on the composition of the sampled particles are being performed and will be presented along with analyses of the meteorological conditions for the three locations under study.
A43A-0886
North Atlantic Measurements of DMS Air/Sea Gradient and Eddy Covariance Flux Using API- CIMS
Dimethylsulfide (DMS) air/sea concentrations and eddy covariance fluxes were measured aboard the R/V Knorr in the North Atlantic Ocean in July 2007. The cruise track extended from Iceland to Woods Hole, MA. Winds were largely westerly over the cruise track and varied from 1-16 m s-1. The meteorological conditions were cold and cloudy, with some periods of fog and rain. Atmospheric DMS levels were measured by atmospheric pressure chemical ionization mass spectrometry (API-CIMS). Seawater DMS levels were measured by API-CIMS using a membrane equilibrator fed by the ship's bow pumping system. DMS levels ranged from 2-40 nM in seawater and 85-5500 ppt in air, with the highest levels northward of the subpolar front, in the North Atlantic spring bloom. DMS flux exhibited the same trend, with fluxes ranging from 1-324 μmol m-2 d- 1. Gas transfer coefficients (k) for DMS were computed from the data. Preliminary analysis indicates that k obtained during this study shows a stronger dependence on wind speed than those from previous measurements based on DMS fluxes (Marandino et al., 2007; Huebert et al., 2004). This dependence is more similar to those from GASEX (McGillis et al., 2001) than and those predicted by Wanninkhof (1992).
A43A-0887
Atmospheric carbonyl sulfide during the last 2,000 years from analysis of air extracted from Antarctic ice cores
Carbonyl sulfide (OCS) is a long-lived sulfur gas that contributes to the formation of stratospheric sulfate aerosol during periods of volcanic quiescence. In this study, we present OCS measurements from an ice core drilled near the South Pole Remote Earth Science and Seismic Observatory (SPRESSO). The SPRESSO core was dry-drilled to a depth of ~300 m and the deepest sample is from 291 m, at which depth we estimate the OCS gas age to be about 2,150 years before present. When combined with the previous records of OCS from Antarctic ice cores and firn air (Montzka et al., JGR 2004), the current data provide a continuous record of OCS extending beyond the last two millennia. The general agreement between ice cores, firn air, and modern air measurements suggests that polar ice is a valid archive for paleoatmospheric OCS. The average OCS mixing ratio of the SPRESSO data is 336∓28 ppt (∓1σ, n=106). The new data reveal variability on centennial time-scales as well as a long-term increasing linear trend of 1.8 ppt per hundred years. OCS levels reach relative highs at the peaks of Medieval Climate Anomaly (MCA) and Little Ice Age (LIA), which stand out as periods of variability during the general climatic stability of the late Holocene. The OCS peak coincident with the height of the MCA measures about 350 ppt and appears to be a result of a long term increasing trend that correlates with increasing temperatures between 600 C.E. and 1100 C.E. The following 400 years is characterized by stabilization of and a subsequent drop in OCS. OCS starts to increase again around 1500 C.E., approaching 400 ppt at the peak of the LIA to reach the highest levels prior to the 20th century. The SPRESSO data do not contradict prior estimates of the impact of anthropogenic emissions on the OCS burden that pushed the tropospheric OCS levels to about 500 ppt during late 20th century.