A43C-0054 1340h
An Integrated Meteorological and Air Quality Modeling Study of the Effect of Complex Terrain on the Regional Transport and Transformation of Air Pollutants
Terrain influences wind direction and speed in both its horizontal and vertical components. Vertical transport of air pollutants into the middle troposphere is potentially important for regional and global scale chemistry. Three factors have been identified that have the potential to affect vertical transport of air pollutants: synoptic scale weather systems, buoyancy, and mountain wind flow over complex terrain. Simulations were made to investigate the relative importance of the effects of complex terrain on vertical transport for the Sierra Nevada Mountains in the western United States. The online coupled meteorological - atmospheric chemistry model MM5-chem was used. The simulations showed that the complex terrain has an important effect on the air pollutant's vertical transport over the regional scale. This vertical mixing reached over 5 km above ground level. It appears that the vertical transport was caused by the terrain forced flow, which is affected by the mountain peak height and the complexity of the mountains in the downwind direction. Furthermore, analysis of the mixing ratio distributions of emitted and photochemically produced air pollutants, such as HNO$_{3}$, CO, NO$_{2}$, and HCHO, showed that these were transported to the upper troposphere by the vertical motion.
A43C-0055 1340h
Transpacific and Regional Atmospheric Transport of Anthropogenic Semivolatile Organic Compounds to Cheeka Peak Observatory During the Spring of 2002
Ambient high-volume (hi-vol) air samples were collected between March 15th and May 30th, 2002, at Cheeka Peak Observatory (CPO), located on the tip of the Olympic Peninsula, Washington State. This sampling campaign was in conjunction with the 2002 Inter-Continental Transport and Chemical Transformation (ITCT 2K2) Campaign and the Photochemical Ozone Budget of the Eastern North Pacific Atmosphere (PHOEBA2) experiment. The anthropogenic semi-volatile organic compounds (SOCs) measured during this time period included polycyclic aromatic hydrocarbons (PAHs) and various U.S. current-use and historical-use pesticides. The total PAH concentration ranged from 0.480-4.49 ng/m3, which is comparable to other remote sites throughout the globe. Ten pesticides (hexachlorobenzene, dacthal, chlorothalonil, heptachlor, trans-nonachlor, cis-nonachlor, endosulfan I, triallate, trifluralin, and mirex) were also measured and their concentrations (0.104-57.0 pg/m3) were comparable to other remote sites and less than agricultural areas. Gas-phase/particle-phase partitioning was explored, with significant correlation to temperature found with endosulfan I and retene and the possible relationship at CPO of low TSP concentration and the concentration of non-exchangeable compounds in the particle phase. Principal Component Analysis, as well as a t-test, showed there were elevated concentrations of anthropogenic SOCs measured during possible Trans-Pacific events on March 15th-16th, March 27th-28th, and April 22nd-23rd, 2002, that were identified using the GEOS-CHEM model. The potential sources of these compounds at CPO were determined using diagnostic ratios of their concentrations, back trajectories calculated using HYSPLIT4, local meteorological conditions, and U.S. pesticide use data. Additional data is needed to confirm the sources of anthropogenic SOCs at CPO during regional and Trans-Pacific atmospheric transport events.
A43C-0056 1340h
Atmospheric Photooxidation of Fluorotelomer Alcohols: A Global Source of Long Chain Perflurinated Carboxylic Acid Pollution?
Humans and animals in urban and remote locations are contaminated with trace amounts of persistent and bioaccumulative perfluorinated carboxylic acids (PFCAs) [1-3]. There are no known natural sources of long chain PFCAs, these compounds are not expected to be mobile in the environment, and it is puzzling that they are observed in remote locations. Fluorotelomer alcohols (FTOHs) are a class of industrially important chemicals with the general formula C$_{x}$F$_{2x+1}$CH$_{2}$CH$_{2}$OH that have been observed in the atmosphere. The atmospheric oxidation of FTOHs is a potential source of PFCAs. Smog-chamber studies of the kinetics and mechanism of the OH radical initiated degradation of FTOHs have been conducted [4]. It was observed that reactions of HO$_{2}$ with C$_{x}$F$_{2x+1}$C(O)O$_{2}$ radicals formed during FTOH oxidation are a source of PFCAs [5]. The reactions proceed by 3 pathways leading to formation of C$_{x}$F$_{2x+1}$C(O)OOH and O$_{2}$, C$_{x}$F$_{2x+1}$C(O)OH and O$_{3}$, or C$_{x}$F$_{2x+1}$C(O)O radicals, OH radicals and O$_{2}$. In the presence of excess of NO$_{x}$, acid formation was not observed, but evidence for the existence of a previously unrecognized stabilized alpha- hydroxy peroxy radical was found. The likelihood that FTOHs contribute significantly to the observed global budget of PFCAs will be the subject of this presentation. {\it References} 1. Masunaga, S., Kannan, K., Doi, R. Nakanishi, J. Giesy, J.P. Levels of perfluorooctane sulfonate (PFOS) and other related compounds in the blood of Japanese people. Organohalogen Compounds (Dioxin 2002). 59, 888 - 891 (2002). 2. Martin, J.W., Smithwick, M.M., Braune, B.M., Hoekstra, P.F., Muir, D.C.G., Mabury, S.A. Identification of Long-chain Perfluorinated Acids in Biota from the Canadian Arctic. Environ. Sci. Tech. 38, 373-380 (2004). 3. Kannan, K Choi, J-W., Iseki, N., Senthilkumar, K., Kim, D.H., Masunaga, S., Giesy, J.P. Concentrations of perfluorinated acids in livers of birds from Japan and Korea. Chemosphere. 49, 225 - 231 (2002). 4. Ellis, D.A., Martin, J.W., Mabury, S.A., Hurley, M.D., Sulbaek Andersen, M.P., Wallington, T.J. Atmospheric lifetime of fluorotelomer alcohols. Environ. Sci. Tech. 37, 3816-3820 (2003). 5. Sulbaek Andersen, M.P., Hurley, M.D., Wallington, T.J., Martin, J.W., Ellis, D.A., Mabury, S.A. Atmospheric chemistry of C2F5CHO: mechanism of the C2F5C(O)O2 + HO2 reaction. Chem. Phys. Lett. 381, 14-21 (2003).
A43C-0057 1340h
Measuring Anthropogenic Semi-volatile Organic Compounds in Eurasian Air Masses at Okinawa Japan
High volume air sampling was conducted at a remote site in Okinawa, Japan to determine the chemical composition of Eurasian air masses during a six week campaign from March 19 to May 1, 2004. The sampling site is located on the northwestern tip of the island of Okinawa (26$^{o}$52$\prime$ N, 128$^{o}$15$\prime$ E, 60 masl). The air masses influencing the site change from marine air to continental air from Eurasia during the spring months. The presence of 84 anthropogenic semi-volatile organic compounds (SOCs) was investigated: including 32 organochlorines, 18 polycyclic aromatic hydrocarbons (PAHs), 12 polychlorinated biphenyls (PCBs), 11 carbamates, 5 organophosphates, and 6 s-triazines. They represent emissions from combustion (PAHs), agricultural (pesticides), and industrial (PCBs) sources. The gas phase was collected using a combination of polyurethane foam (PUF) and XAD-2 resin, while the particle phase was collected using quartz fiber filters. Over the six week campaign, 18 samples were taken in 24 hour sampling periods with an average flow rate of 0.43 m$^{3}$/min. The samples were extracted using accelerated solvent extraction and the extracts analyzed by GC/MS (EI and ECNI). Air trajectories were calculated using data from NOAA$\prime$s HYSPLIT and imported into the ARC/GIS program for spatial representation. The chemical composition of the sampled air masses was determined and potential sources identified.
A43C-0058 1340h
Long-Range Atmospheric Transport of Semi-volatile Organic Compounds to Cheeka Peak Observatory in Conjunction with Asian Dust and Smoke Events of 2003
The atmospheric transport of anthropogenic semi-volatile organic compounds (SOCs) from Asia to the United States west coast may be important for determining the chemical fate and environmental impacts of these compounds. SOCs were measured using a high volume air sampler located at Cheeka Peak Observatory (CPO) in the state of Washington on the tip of the Olympic Peninsula from January 28th, 2003 to December 10th, 2003. Throughout this time period, dust and smoke events were observed during June 2-6th and August 5th of 2003 by the aerosol monitoring system NAAPS (Navy Aerosol Analysis and Prediction System). Air samples were collected with a quartz fiber filter to trap the particulate phase SOCs and a polyurethane foam and XAD-2 resin combination to trap the gas phase SOCs. The samples were accelerated solvent extracted and analyzed using Electron Impact and Electron Capture Negative Ionization Gas Chromatographic Mass Spectrometry. The target analytes were anthropogenic SOCs including markers for incomplete combustion (polyaromatic hydrocarbons), agriculture (pesticides such as organochlorines, organophosphates, and triazines), and industrial and urban sources (polychlorinated biphenyls). Potential source locations were determined using NOAA hysplit back trajectories along with satellite and meteorological data.
A43C-0059 1340h
Mercury Flux Studies on Urban Surface Covers
In an effort to advance the state-of-art understanding of mercury's global transport, a study was conducted to measure and evaluate the in-situ flux of total mercury from common urban surfaces (weathered blacktop, compact soil, grass, street runon) with spatial (3 km radius) and seasonal change, and quantify the affect of irrigation on flux from blacktop and street runon. Additional experiments examined the relative flux contribution from each surface under uniform meteorological conditions. Average seasonal flux (ng/m2-hr) measurements are as follows: 0.569 (Winter) 0.274 (Spring) for grass; 0.0910 (Winter) 0.612 (Spring) for blacktop; 1.750 (Winter) 7.451 (Spring) for soil. Relatively high terrestrial adsorption/deposition (-1.5 ng/m2-hr) occurred for grass during the early morning (3am to 7 am) in Winter. No adsorption occurred for soil in either season. Using multi-regression analyses, statistically significant (p = 0.05) time series relationships were found between Hg flux and (1) UV and total solar radiation (2) surface temperature and (3) surface moisture for each cover type. For Winter flux contribution studies, 76% of total Hg (mass) emitted at this site came from soil, 14% from grass, and 10% from blacktop. In the Spring study, emissions increased an additional 3% for soil and grass. Artificial irrigation experiments were performed on blacktop and street runon to (1) determine if wet deposition delivers a pool of oxidized mercury that is available for reduction and release, and (2) simulate release mechanisms of Hg during wet weather events. No statistically significant difference (p = 0.05) in flux was found when de-ionized (DI) and rain water were separately applied to blacktop and street runon. This suggests that oxidized mercury forms in rainwater do not increase flux for blacktop and street runon during wet weather events. However, DI and rainwater create, on average, a 7-fold increase in flux immediately after irrigation from preexisting mercury on these surfaces. Geochemical Hg de-sorption and physical displacement of air-containing-Hg by H20 are the primary methods of Hg release and resulting flux. Our analyses also show that no statistically significant spatial variability in flux exists for the studied urban area on this scale.
A43C-0060 1340h
UK Landfill Gas Emissions from a Field Campaign in Southwestern England during July/August 2004
Anthropogenic emissions of long-lived halocarbons, namely chlorofluorocarbons (CFCs), hydrofluorocarbons (HCFCs), methyl chloroform (CH$_{3}$CCl$_{3}$), and carbon tetrachloride (CCl$_{4}$) represent the largest source of atmospheric chlorine. A large fraction of the end uses of these compounds have resulted in the dumping of chlorine-containing equipment and materials in waste sites from which leakage is now occurring. Previous work at two US landfills in Eastern Massachusetts has shown that landfill gas emissions may be a significant source of atmospheric chlorine. This idea was further explored during a field campaign in southwestern Britain in July/August 2004. Flask samples were taken at several landfills with varying waste composition, landfill age, and basin geology. The flasks were analyzed for CFC-12, CFC-11, CFC-113, CH$_{3}$CCl$_{3}$, and CCl$_{4}$ using GC-ECD. Results will be shown for the UK landfills as well as a comparison between the US and UK sites.
A43C-0061 1340h
Measurements of NO$_3$ and N$_2$O$_5$ in the Polluted Subarctic Atmosphere: A Seasonal Perspective From Multi-year Observations in Fairbanks, AK
Nitrate radical is both an important oxidant in the nighttime atmosphere and an important intermediate in the removal of NO$_x$ from the atmosphere. Although its source is understood (the reaction of NO$_2$ with ozone), questions still surround the budget of nitrate resulting from its many possible sinks. Further complicating the situation is the equilibrium between NO$_2$, NO$_3$, and N$_2$O$_5$, which becomes important at low temperatures when the equilibrium shifts toward N$_2$O$_5$. We report measurements of the sum of NO$_3$ and N$_2$O$_5$ made with a cavity ring-down spectroscopy-based instrument over the past two years in Fairbanks, AK, along with auxiliary CO, O$_3$, and meteorological data. The sum of NO$_3$ plus N$_2$O$_5$ is detected by heating ambient air to dissociate N$_2$O$_5$ to NO$_3$; absorption of NO$_3$ at 662 nm is then used to detect the total NO$_3$ radical concentration. We term the sum of NO$_3$ + N$_2$O$_5$ the total nitrate radical species. We observe a clear correlation between the total nitrate radical species mixing ratio and the type of airmass situated over Fairbanks. Values below the detection limit are measured for both clean and very polluted airmasses. Measurable amounts are observed at night in moderately polluted airmasses that result from the mixing of background, ozone-rich air masses with polluted, NO$_x$-rich airmasses. With measurements in mid-winter, late winter, and spring, we can begin to construct a picture of the seasonal role nitrate radical plays in the chemistry of Subarctic regions. The highest values measured (250 pptv total nitrate radical species) were observed in late winter, with lower values observed in both winter and spring. Both mid-winter and springtime low levels can be understood by considering meteorological conditions. In mid-winter strong inversions dominate, trapping nitrate radical species close to the ground where surface losses are likely large. In springtime, significant daytime solar heating causes vertical mixing and dilutes pollutants rapidly, slowing production of nitrate radical species. Estimates of the nitrate radical species lifetimes in these various environments are discussed.
A43C-0062 1340h
Chemical age of air Masses Determined From Ambient Volatile Organic Compound Measurements During NEAQS 2004
During July and August of 2004, as part of the New England Air Quality Study (NEAQS 2004), volatile organic compounds (VOCs) including hydrocarbons, oxygenated hydrocarbons and alkyl nitrates were measured aboard the NOAA research vessel Ronald H. Brown. Samples were acquired at half hourly intervals without storage and analyzed immediately by an automated GC-FID and GC-MS system. The observed ratios of VOC species with different photochemical loss rates, or the ratios of oxidation products and their precursors, can be employed as indicators for chemical age of air masses encountered. Several of these ratios have been compared to those expected from OH photochemistry and photolysis. Time scales inferred are shown to be in reasonably good agreement with transport times obtained from backward trajectory calculations. The choice of appropriate ratios for the estimation of air mass chemical age (from hours to days) is discussed. The influence of regional backgrounds of relevant VOC species, and nighttime chemistry are also pointed out.
A43C-0063 1340h
Chemical processes in a smoke plume from a savanna fire
Gaseous emissions from wildfires include a wide range of organic compounds, including oxygenated VOCs, and nitrogen oxides. Chemical processes in young plumes from fires significantly modify the initial emissions. Field measurements performed in the smoke plume from the Timbavati fire during SAFARI 2000 using the Airborne Fourier Transform Infrared Spectrometer (AFTIR) onboard the University of Washington's Convair-580 aircraft show significant increases in the enhancement ratios of ozone and acetic acid with respect to CO during the first hour following the emission into the atmosphere. Decreases in enhancement ratios have been measured for a number of hydrocarbons. Investigating the chemical reactions that lead to these fast changes helps to improve our present understanding of tropospheric photochemistry. Here, we present results from model simulations using a detailed photochemical box-dilution model constrained to the field observations. Using known photochemical processes, the model underestimates the observed production of ozone and acetic acid, even if radiative effects of the smoke aerosol and uncertainties in the emissions are taken into account. Introduction of a recently proposed heterogeneous reaction between NO$_2$ and methanol significantly improves the comparison for ozone. Several potential sources for acetic acid are discussed including production of acetate in the particulate phase and subsequent degassing. These investigations point to the importance of the interactions between the gas and aerosol phase for the photochemistry in young smoke plumes and potentially in other environments, and highlight the importance of further field and laboratory experiments.
A43C-0064 1340h
Regional and USA Emissions of Methyl Chloroform and Other Gases Inferred From AGAGE Measurements at Trinidad Head, California Since 1995
CH3CCl3, CCl2F2, CCl3F, CCl4, CClF2CCl2F, N2O, CH4 and CHCl3 have been measured 36 times daily at Trinidad Head, California (41N, 124W) since 1995. The effects of regional emissions of these gases are clearly seen in the measurements. Back trajectory calculations show that the pollution events are associated with trajectories over California and the neighboring States. Using a 3D trajectory model and population densities as proxies for the distribution of the emissions, reasonable agreement is found between the emission inventory for CH3CCl3 and the observations. The estimated regional emissions have decreased by factors of approximately 10 and 3 for CH3CCl3 and CCl2F2 respectively. Similar estimates are obtained by considering ratios to methane pollution events and using the gridded methane emission estimates from the EDGAR database. Combining our estimates with those obtained in the Northeastern U.S. by Barnes at al. in 2003, U.S. emissions of CH3CCl3 and other measured halocarbons are further estimated.
A43C-0065 1340h
Emission Measurements of Mono and Sequiterpenes From Loblolly Pine ({\it Pinus taeda}) Using a Dynamic Branch Enclosure Technique
Biogenic VOC's such as monoterpenes and sequiterpenes are emitted from forest vegetation and are known precursors for secondary organic aerosols. However, there is very little information quantifying the emission rates of these VOC's and the changes in emission rate due to environmental and physiological factors, especially for oxygenated terpenes and sesquiterpenes. The goal of our research to quantify mono and sesquiterpene emissions from loblolly pine growing the Duke Forest in Chapel Hill, NC. FEP Teflon film enclosures were carefully placed on rapidly growing full sun branches throughout the year. Ambient air was scrubbed of ozone and purged through the enclosure at approximately 25 liters per minute. The incoming air was also cooled using an ice bath and water condensation was trapped and taken out of the air stream. Air temperatures inside of the enclosure stayed within 4 degrees C of the ambient air when in the full sunlight. Tenax filled tubes were used to sample the outflow from the branch enclosure. Compounds were quantified and identified by thermally desorbing the tubes on to a GC/MS system. The most abundant compounds found were alpha-pinene, beta-pinene, limonene, beta-phellandrene, longifolene, beta-caryophylene, and alpha-humulene. Our measurements in the fall and winter indicated substantially more sesquiterpenes (primarily beta-caryophylene) than monoterpenes (primarily alpha-pinene). These results indicate sesquiterpene emissions may be a large part of VOC emissions from Loblolly pine. Sequiterpenes may be missed in ambient air studies due to their rapid reaction with ozone. Therefore, a large quantity of high aerosol forming VOCs may be missed in biogenic VOC emission inventories.
A43C-0066 1340h
Investigation of the importance of injection heights of biomass burning emissions from boreal fires to tropospheric modeling.
Injection heights of biomass burning emissions from the boreal forests of Russia, Alaska, and Canada represent a major uncertainty in modeling their effects on atmospheric composition. There is substantial evidence that emissions from boreal forests are injected in the free troposphere, and even into the lower stratosphere on occasion. However, there is currently no method for parameterizing these injection heights in global models. Simulations with the GEOS-CHEM model show that a substantial fraction of the emissions from boreal fires must be injected above the boundary layer. In this study, we investigate the effects of intense boreal fires in 2002 using the GEOS-CHEM model, using various assumptions for the injection heights. Results are evaluated with CO columns retrieved from the MOPITT satellite instrument, as well as surface data.
A43C-0067 1340h
Fluxes of Short-Lived Organic Halogens Into the Marine Boundary Layer
Recent interest in the contribution of short-lived halogenated gases to stratospheric ozone depletion prompted us to evaluate the fluxes of these gases from the ocean surface into the atmosphere in areas of potentially high convection. We make our evaluation based upon two cruises in the Pacific Ocean, one running from Kwajalein (10 N) to Hawaii (21 N) to Alaska (54 N) to Seattle (48 N) during the fall of 1999 and the other from Guam (12 N ) to Hawaii (21 N ) to Newport, Oregon (44 N), during the spring and early summer of 2004. Although the two cruises do not overlap exactly, they course through similar water masses during nearly opposite seasons. This allows us to make seasonal comparisons of the saturations of these gases and, by extension, evaluate their fluxes relative to their potential to be associated with deep convection. In the Tropical West Pacific, where the potential for convection is highest, spring and summer supersaturations of the very short-lived gases (CH3I, CH2Br2, and CHBr3) were about twice those in the fall, ranging from a mean of 25% for CH2Br2 during the fall to 4300% for CH3I during the spring/summer. In the temperate Northeast Pacific, these gases remained supersaturated at all times, but at lower levels than in the tropics. Their supersaturations during the spring and summer also were about twice those of those in the fall, ranging from 40% for CH2Br2 to 3200% for CH3I. CH3Br, a slightly longer lived gas, behaved differently, remaining undersaturated at around -30% in tropical waters and swinging from a mean of -20% in the fall to +20% in the summer in temperate waters, consistent with seasonality previously observed for this gas in temperate waters.
A43C-0068 1340h
Measurements of C$_{1}$-C$_{5}$ Alkyl Nitrates Using Gas Chromatography/Negative Ion Chemical Ionization Mass Spectrometry
We applied gas chromatography/negative ion chemical ionization mass spectrometry (GC/NI-CIMS) technique for measurements of alkyl nitrates (RONO$_{2}$) in the atmosphere, since it could be sensitive to high electron affinity species as well as selective by making use of the selected ion monitoring detection. In this study, a number of experiments have been made to improve its performance using multi-components RONO$_{2}$ standard gases, which were gravimetrically prepared in high-pressurized gas cylinders. We found that RONO$_{2}$s typically produced [RO-H$_{2}$]$^{-}$ and NO$_{2}$$^{-}$ as their NI-CIMS fragment ions except MeONO$_{2}$ and tert-RONO$_{2}$, producing RO$^{-}$ and NO$_{2}$$^{-}$. Relative abundance of [RO-H$_{2}$]$^{-}$ to NO$_{2}$$^{-}$ showed distinct increasing features as the increase of the carbon numbers of RONO$_{2}$. Based on these results, the instrument, particularly a gas chromatograph, an ion source, and a quadrupole mass filter were optimized to achieve both sensitivity and selectivity simultaneously. Excellent linearity was confirmed in the ppbv regions. The detection limit and precision were in the sub-ppbv range and less than 10% for 7 RONO$_{2}$s studied, respectively. Experimental details, the instrument performance, and the stability of the standard gases will be presented.
A43C-0069 1340h
Iodine Chemistry in the Marine Boundary Layer
The atmospheric chemistry of iodine in the marine boundary layer is important for a number of reasons. These include the role of the iodine oxides IO and OIO in depleting ozone and affecting the HOx and NOx cycles, the activation of chlorine and bromine from sea-salt aerosols, the ability of higher iodine oxides to form new particles in the remote atmosphere, and the enrichment of iodine in marine aerosols and the subsequent transport of this essential dietary element to the continents. In this paper we will report the first observations of I2 in the coastal marine boundary layer, made by Differential Optical Absorption spectroscopy (DOAS). Very large I2 concentrations correlating with low tide indicate that the source is emission from exposed macro-algae. Simple scaling suggests that this coastal emission could approach 2 Tg per year, making it a major contribution to the global iodine budget. During the same campaign, DOAS observations were also made of the halogen oxides IO, OIO and BrO. Pulses of IO and BrO measured at sunrise are strong evidence for heterogeneous processing on sea-salt aerosol. IO and OIO were also observed during the night, most likely produced from the reaction of I2 with NO3 radicals. Laboratory studies of the kinetics and photochemistry of OIO and INO3 will also be reported. Simple modelling shows that the halogen radicals play important roles in ozone depletion, the oxidation of dimethyl sulfide, and the formation of new particles in the marine boundary layer.
A43C-0070 1340h
Regional scale impacts on an elevated high ozone episode in the Alps
Ozone events in urban regions are a major atmospheric pollution problem in Europe. During the summer of 1999, a field campaign GRENOble PHOTochemistry (GRENOPHOT) was held in the Grenoble metropolitan region, in the French Alps, in order to obtain high resolution (spatial and temporal) measurements for air quality modeling assessment. The meteorological and atmospheric chemistry simulations were validated using both near ground and atmospheric profile measurements (e.g. lidar measurements of ozone) during the Intensive Observation Period (IOP): observations 25$^{th}$-27$^{th}$ July. Of particular interest were a series of lidar which showed between 2000 and 2500 meters elevated ozone levels during the night of 26$^{th}$ and 27$^{th}$. In order to understand the origin of these high ozone levels we apply a series of mesoscale models focusing from Europe to the Rh\^{o}ne-Alpes region and down to the urban scale to distinguish local ozone production from ozone transported. At the European scale MM5 was used to simulate the meteorological fields coupled with the Chemistry Transport Model CHIMERE with a 27-kilometer mesh resolution covering Central Europe. At the regional and local scales, the air quality model METeorological PHOtochemistry MODel (METPHOMOD) was used with a 6 km mesh resolution for the regional grid and at a 2 km resolution mesh for the smaller urban grid. This chain of mesoscale models is applied with a nesting procedure which couples the individual model simulations. Ozone mixing ratios, run at the large scale, demonstrated the advection of ozone at higher altitudes during the night and the last day of the IOP from the Mediterranean sea. Moreover, the contribution of NOx and VOC clearly showed an important contribution to the near surface ozone mixing ratio. This chain of nested models improves the prediction of the vertical ozone distribution and explains the source of the ozone measured by lidar in the free troposphere.
A43C-0071 1340h
Measurement of Atmospheric Formaldehyde by Laser-Induced Fluorescence
The development of a laser-induced fluorescence (LIF) formaldehyde (HCHO) detection instrument capable of measuring parts-per-trillion-by-volume (pptv) levels of formaldehyde in ambient air is presented. This instrument is part of a multispecies detection system designed to measure a variety of species (the other species in this initial version are NO and NO$_2$) important to photochemistry and atmospheric composition in a compact, robust package suitable for airborne and other field measurements. A preliminary version was deployed on the Intercontinental Chemical Transport Experiment - North America (INTEX-NA) in the summer of 2004. This approach employs excitation of the lowest-lying electronic state of formaldehyde along the A$^1$A$_2$ $\leftarrow$ X$^1$A$_1$ transition at 353.16 nm and measurement of fluorescence in the 400-450 nm range. The instrument samples ambient air at reduced pressure in a White cell and operates at kHz pulse repetition frequencies. We have identified no significant chemical interferences for this measurement scheme.
A43C-0072 1340h
Reanalysis of HOx Model Predictions Versus Observations: Adequacy of Modeling Approaches
A unified analysis of the body of HOx observations from the Penn State Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) instrument is presented. Although prior analyses of individual field campaigns have been beneficial in revealing important components of the HOx budget previously neglected or unrecognized, a single integrated analysis is now desirable to establish consistency between data sets and the modeling approach. This analysis makes use of early HOx data sets that have been adjusted with minor corrections to the measurements to account for the evolution of understanding of instrument sampling characteristics. Additionally, a single photochemical model with current reaction rates is used for the predictive analysis. Results are examined for consistent trends in model/measurement agreement related to budget parameters such as HOx primary production. Trends are also inspected for possible artifacts related to parameters such as the solar zenith angle, or in the modeling approach itself. Under specific conditions, we show that extreme air mass heterogeneity can have a profound impact on conclusions regarding HOx dependencies on NOx concentrations. For these conditions (e.g. flights through aircraft contrails) the typically used 1-minute data average is not adequate, and the data analysis must proceed using much shorter time resolutions (e.g. 1-second). Other environmental conditions contributing to air mass heterogeneity at smaller time and spatial scales are examined for similar influences on the analysis.
A43C-0073 1340h
Measurements of Peroxy Radicals in the UK Summer Heatwave of 2003
The sum of organic peroxy radicals and HO$_2$ was measured with a peroxy radical chemical amplifier (PERCA) during the Tropospheric ORganic CHemistry experiment (TORCH) in August 2003 on a ground based platform at a site in the South of England. Measurements of peroxy radicals, which act as intermediates and chain carriers in the gas phase radical chain oxidation of volatile organic compounds, can be used to determine the in-situ production rate of ozone. Record temperatures (up to 39 degrees Celsius or 100 degrees Fahrenheit) were experienced in the UK during the second week of August and this work focuses on the significance of peroxy radical levels to ozone production during this period. Maximum total peroxy radical mixing ratios over the week of the heatwave were up to five times the levels recorded in the periods before and after the hot weather while ozone mixing ratios reached 152ppb - well above the European safety threshold of 90ppb. A range of VOCs was also measured and data from fifteen alkenes, including the biogenic compound isoprene, were used to calculate peroxy radical production rates. On the day of the highest maximum temperature isoprene was found to have the greatest contribution towards peroxy radical production via alkene ozonolysis over a significant part of the day. The extent to which the ozonolysis of alkenes was important in the production of peroxy radicals and implications for ozone production will be discussed.
A43C-0074 1340h
Case study of an ozone titration event in Narragansett at the 28th of July during the NEAQS-ITCT 2004 Campaign
During the New England Air Quality Study - Intercontinental Transport and Chemical Transformation (NEAQS-ITCT) 2004 Campaign we performed measurements with Multiple Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) at several sites in the northeast of the USA. Ultraviolet spectra of scattered sunlight were measured continuously at five elevation angles, including the zenith. Analysis using the DOAS technique yields slant column densitites, and with radiative transfer modelling, vertical column densities of several trace gases, including NO$_{2}$. At Narragansett, RI ozonesonde profiles were observed daily. On July 28 we observed reduced light intensity in the presence of surface fog and deep clouds, and elevated NO$_{2}$ concentrations throughout the day. The ozone profile at 1830 UTC (1430 local time) showed an absence of ozone at the surface, with values increasing to approximately 65 ppbv above 300 m. A capping inversion trapped pollutants in this layer over an area extending from central Long Island to Boston, MA. Maximum 8 hour average ozone mixing ratios from monitors in Rhode Island were remarkably low, below 11 ppbv for this day. The slant column density for NO$_{2}$ was greater than 4 \cdot 10$^{16}$ molecules per cm$^{2}$ for the lowest elevation angle (3$^{\circ}$). The light intensity at mid-day was extremely low, comparable to twilight conditions. Analysis of the spectra suggests that aerosol scattering was also high near the surface. Together, these observations suggest that ozone titration took place even in mid-afternoon during this event.
A43C-0075 1340h
Evidence of Lightning NOx and Convective Transport of Pollutants in Satellite Observations Over North America
Column observations of NO$_{2}$ by GOME and CO by MOPITT over North America and surrounding oceans for April 2000 are analyzed using a regional chemical transport model. Transient enhancements in these measurements due to lightning NO$_{X}$ production or convective transport are examined. Evidence is found for lightning enhancements of NO$_{2}$ over the continent and western North Atlantic and for convective transport enhancements of CO over the ocean. The two independent satellite measurements show consistent enhancement related to convective events. Model results suggest that the enhancements are particularly large in the lower troposphere due to convective downdrafts of lightning NO$_{X}$ and shallow convection of CO, implying that low altitude aircraft in situ observations are potentially critical for evaluating the model simulations and validating satellite observations of these transient features
A43C-0076 1340h
In-Situ Measurement of $\Sigma$ANs During INTEX-NA
Alkyl and multifunctional nitrates ($\Sigma$ANs), produced by reactions of peroxy radicals with NO and reactions of the NO3 radical with alkenes, have previously been observed at high mixing ratios and comprising large fractions of NOy and NOz at the surface. To date there have been no observations of $\Sigma$ANs above the surface. $\Sigma$ANs were measured in real time aboard the NASA DC8 during INTEX-NA (6/1/04-8/14/04) by Thermal Dissociation Laser Induced Fluorescence (TD-LIF). Aircraft flights during INTEX-NA included extensive characterization of the continental and marine boundary layers as well as frequent vertical profiles. Here we describe the $\Sigma$AN mixing ratios observed and show some critical comparisons to measurements of speciated nitrates reported in prior studies. Correlations between $\Sigma$ANs and other products of hydrocarbon oxidation, such as formaldehyde, are used to place constraints on alkyl nitrate yields in the boundary layer.
A43C-0077 1340h
Measurements of Non-Methane Hydrocarbons as Oxidant Probes over the Greenland and Norwegian Seas
Non-methane hydrocarbons (NMHCs) are ubiquitous in the marine troposphere at trace concentrations. They have long been postulated to originate from the degradation of dissolved organic matter (DOM) in surface waters, and furthermore may elucidate the role of various oxidants in the troposphere. Whole air, DOM in surface waters, and organic aerosols were simultaneously sampled on the RV Polarstern ARK-XX cruise in the Greenland and Norwegian seas in the summer of 2004. Initial results focused on the air samples, which were collected in electropolished stainless steel canisters and analyzed for NMHCs using a cryogenic preconcentration-GC apparatus constructed in-house. These NMHC results indicate the relative importance of different oxidants in the air parcels sampled. We will discuss the potential implications for the long-term goal of understanding the processes by which volatile organic compounds may originate from marine DOM.
A43C-0078 1340h
Convective Transport of CO During CRYSTAL-FACE: Modeling Results
Several atmospheric tracer measurements were made during NASA's CRYSTAL-FACE project in Key West, Florida during July of 2002. One of the primary goals of CRYSTAL-FACE was to measure the effect of convective systems, in particular cirrus anvil blow off, on high altitude tracer mixing ratios. Carbon monoxide (CO) was measured both in the boundary layer and in the upper troposphere. Generally, CO was found to be slightly enhanced, relative to the free troposphere, in the upper tropospheric convective cirrus clouds. These in situ results have been evaluated using DHARMA, a mesoscale model and will be discussed in this presentation.
A43C-0079 1340h
Modeling the Atmospheric Formation of Reactive Mercury in Florida and the Great Lakes
Reactive mercury in the troposphere is affected by a complex mix of local emissions, global-scale transport, and gas and aqueous-phase chemistry. Here, we describe a modified version of the EPA model for urban/regional air quality (CMAQ) to include the chemistry of mercury, and model applications focusing on the Great Lakes region and on South Florida. The University of Michigan modifications to CMAQ include an integrated numerical solver for gas-phase and aqueous photochemistry, improved representation of in-cloud photolysis rates, and up-to-date reaction schemes for mercury chemistry. Reactive mercury is produced primarily by gas-phase reactions. Aqueous reactions tend to convert reactive mercury back to its elemental form, but the most important aqueous reactions (with HO2 and O2-) are problematic (Gartfeld and Jonnson, 2003). Model results suggest that gas-phase conversion from elemental to reactive mercury can lead to high concentrations of reactive mercury in the middle troposphere. Reactive mercury in the lower troposphere is removed more rapidly through both wet and dry deposition and potentially through aqueous conversion to elemental mercury. Model results are compared with a suite of comprehensive gas and aerosol measurements performed in Michigan and during aircraft measurements in S. Florida. Model results suggest that direct emission of reactive mercury contribute to atmospheric deposition in source regions. This work has been funded wholly or in part by the United States Environmental Protection Agency Office of Research and Development. It has been subjected to peer review and approved for publication.
A43C-0080 1340h
CO and O3 Concentrations During a Saharan Dust Storm
The NOAA Center for Atmospheric Sciences (NCAS) conducted a combined atmospheric and oceanographic experiment aboard the NOAA Ronald H. Brown ship to characterize the physico-chemical evolution of the Saharan Aerosol Layer during its long-range transport into the eastern seaboard of the United States and the Caribbean and to quantify its effects on the regional environment and climate. The NCAS Trans-Atlantic Aerosol and Oceanographic Science Expedition (AEROSE-04) departed on its 27-day voyage February 29, 2004 from Bridgetown, Barbados and concluded in San Juan, Puerto Rico on March 26, 2004. During AEROSE-04, CO and O3 concentrations were measured to study the effects of Saharan dust on the chemistry of the atmospheric environment. Tropospheric O3 and CO were measured in-situ and on a continual basis during several dust storms that occurred during the month of March. This presentation will highlight the atmospheric measurements of CO and O3 that were taken during the AEROSE-04 mission.
A43C-0081 1340h
The Regional Atmospheric Measurement Modeling and Prediction Program (RAMMPP)
Many parts of the mid-Atlantic region are in violation of EPA air quality standards. Factors that influence air quality in this region include local and regional emissions, synoptic and meso-scale meteorology, and boundary layer chemistry and dynamics. Unfortunately, some of these processes are not well characterized and their fractional contributions to air pollution in the region are not well understood. In 1992, in response to this challenge, a consortium of mid-Atlantic states initiated a research program called Regional Atmospheric Measurement Modeling and Prediction Program (RAMMPP) to conduct holistic, long-term air quality studies in the region. RAMMPP aims at developing a state of the art scientific research tool to gain an informed understanding of the factors controlling air quality over the mid-Atlantic region and involves four elements: i) Forecasting; daily air quality forecasts for ozone are issued from May through September (http://www.atmos.umd.edu/$\sim$forecaster/ozone\_fcst.html). ii) Meso-scale Modeling; year-round daily, real-time numerical weather forecasts are produced for the mid-Atlantic area using the meso-scale model 5 (MM5) operating on a triply (36/12/4 km) nested grid with innermost domain centered on the Baltimore-Washington urban corridor (http://www.atmos.umd.edu/$\sim$Emm5). iii) Measurements; observations of meteorology, selected trace gases, and aerosol chemistry, microphysics, and optical properties are made at selected surface sites throughout the region. Further-more, measurements of upper air meteorology and chemistry are made using radio-sondes, profilers, and an instrumented light aircraft (http://www.atmos.umd.edu/$\sim$RAMMPP/). iv) Chemical Transport Modeling; the three elements above are combined in an emissions and chemical transport modeling program using the SMOKE and EPA CMAQ framework, constrained and evaluated using assimilated field data. Noteworthy RAMMPP results include the discovery that aerosols can accelerate photochemistry, the improvement of GOME SO2 retrievals to make them usable for air pollution detection, the observance of a Quebec forest fire plume over the mid-Atlantic, thereby demonstrating the role of long range pollution transport on air quality in the northeast US and measurements during the 2003 electrical blackout that show the impact of power plant emissions on ozone and aerosols. Here we present a chemical climatology of the mid Atlantic region based on analysis of all data generated since the inception of RAMMPP, with special emphasis on airborne measurements.
http://www.atmos.umd.edu/~RAMMPP/
A43C-0082 1340h
Measurements of N$_{2}$O$_{5}$, NO$_{2}$ and O$_{3}$ at a Site in the San Francisco Bay Area
We present measurements of N$_{2}$O$_{5}$, NO$_{2}$ and O$_{3}$ made during January 2004. N$_{2}$O$_{5}$ was measured by thermal dissociation to yield NO$_{3}$, which was then detected by laser-induced fluorescence (LIF). NO$_{2}$ was also measured by LIF, and O$_{3}$ was measured using a commercial uv photometric analyzer. The site is a forest research reservation adjacent to Briones Regional Park in the coastal hills of Contra Costa County, 30 km northeast of San Francisco. Mixing ratios of N$_{2}$O$_{5}$ ranged up to 200 ppt at night, with calculated steady state lifetimes of 5 to 30 minutes. Implied HNO$_{3}$ production rates by heterogeneous N$_{2}$O$_{5}$ hydrolysis as well as ongoing improvements to the N$_{2}$O$_{5}$ instrument will be discussed.
A43C-0083 1340h
Actinic Flux Measurements for the Central California Ozone Study
The formation rates and lifetimes of many tropospheric chemical species depend on the photolysis rate parameters of nitrogen dioxide, ozone, formaldehyde and other compounds. A compound's photolysis rate parameter depends on its wavelength dependent absorption coefficients, its quantum yields and the spherically integrated solar radiation, also know as actinic flux. However in many field studies actinic flux is estimated from models or flat plate radiometer measurements. A major goal of this project was to determine the importance of measuring actinic flux as part of a major field study. Measurements of actinic flux were made during the summer of 2000 as part of the Central California Ozone Study (CCOS). Spectral-radiometers with hemispherical integrating collectors were located at the University of California at Davis (UC-Davis), Sunol, California, and the Desert Research Institute in Reno, Nevada. This study focused on comparing actinic flux measurements made during two high ozone episodes occurring at the end of July and during mid-September. The measured actinic flux was compared with total horizontal flux data from shadowband radiometers co-located at UC-Davis. Although actinic flux and total horizontal flux are different quantities, at lower wavelengths comparisons are reasonable due to the greater scattering of radiation. The agreement between the total horizontal flux and actinic flux measurements was close for wavelengths below 332 nm and was within 7 x $^{12}$ photons cm$^{-3}$ s$^{-1}$ while above this wavelength they diverged to differences of 3.7 x 10$^{14}$ photons cm$^{-3}$ s$^{-1}$ or greater. The measured actinic flux and the actinic flux calculated from models including the delta-Eddington approach and the standard Peterson flux agreed better for the September episode then for the July episode.