A23A-0761 1340h
Analysis of the Weekend Effect in Ozone in Central California Using Speciated NO$_{y}$ and VOC Measurements
The Sacramento Valley and Mountain Counties of California routinely violate the federal 8-hour O$_{3}$ standard between May and October. We present an analysis of the weekend effect in O$_{3}$ at several sites in the area for the last five years, showing that sites in the valley generally have higher weekend ozone while sites downwind have lower ozone. Long term NO$_{x}$, NO$_{y}$, VOC and O$_{3}$ observations at UC Blodgett Forest and detailed measurements of composition at Granite Bay during summer 2001 and at Big Hill during 2003 are used to examine our understanding of the mechanisms responsible for the weekend/weekday differences in O$_{3}$. We will describe weekend/weekday differences in NO$_{2}$ mixing ratio and in VOC reactivity. Ratios of HNO$_{3}$ and peroxynitrates to NO$_{2}$, and relationships among the hydrocarbons will be used to compare and contrast HO$_{x}$ chemistry and the rate of ozone production on weekdays and weekends.
A23A-0762 1340h
REGIONAL ATTRIBUTION OF OZONE PRODUCTION AND ASSOCIATED RADIATIVE FORCING: A STEP TO CREDITING NOx EMISSION REDUCTIONS
The global distribution of tropospheric ozone (O3) depends on the location of emissions of its precursors in addition to chemical and dynamical factors. The global picture of O3 forcing is, therefore, a sum of regional forcings arising from emissions of precursors from different sources. The Kyoto Protocol does not include ozone as a greenhouse gas, and emission reductions of ozone precursors made under Kyoto or any similar agreement would presently receive no credit. In this study, we quantitatively estimate the contribution of emissions of nitrogen oxides (NOx), the primary limiting O3 precursor in the non-urban atmosphere, from specific countries and regions of the world to global O3 concentration distributions. We then estimate radiative forcing resulting from the regional perturbations of NOx emissions. This analysis is intended as an early step towards incorporating O3 into the Kyoto Protocol or any successor agreement. Under such a system countries could obtain credit for improvements in local air quality that result in reductions of O3 concentrations because of the associated reductions in radiative forcing. We use the global chemistry transport model, MOZART-2, to simulate the global O3 distribution for base year 1990 and perturbations to this distribution caused by a 10% percent reduction in the base emissions of NOx from the United States, Europe, East Asia, India, South America, and Africa. We calculate the radiative forcing for the simulated base and perturbed O3 distributions using the GFDL radiative transfer model. The difference between the radiative forcing from O3 for the base and perturbed distributions provides an estimate of the marginal radiative forcing from a region's emissions of NOx. We will present a quantitative analysis of the magnitude, spatial, and temporal distribution of radiative forcing resulting from marginal changes in the NOx emissions from each region.
A23A-0763 1340h
Impact of greenhouse gas emissions reduction in Indonesia: NO2
In this study, we develop scenarios of total air pollution from fossil fuel consumption and its impacts for the 21st century, using an inter-temporal general equilibrium model MERGE. The Model for Evaluating the Regional and Global Effects of greenhouse gas reduction policies (MERGE) is used to project energy consumption and production. We use the base scenarios from IPCC (2000). These scenarios assume that no measures are undertaken to control greenhouse gas emissions. We extend the IPCC scenarios with mitigation scenarios, estimating the air pollution impacts of greenhouse gas emission reduction. The MERGE model was extended to analyze emissions of nitrogen dioxide (NO2), their concentrations, impacts on human health, and economic valuation. To estimate of nitrogen dioxide (NO2) impacts on respiratory symptoms, we calculated the NO2 concentration as derived from nitrogen oxide (NOx). In the baseline scenario, the concentrations of NO2 are rising to 2,263 μg/m3 in 2100. If the Organisation for Economic Co-operation and Development (OECD) countries reduce their emissions, respiratory symptoms among adult's associated with NO2 case would reach the highest to 65,741% of adult population cases by the end of century. If all countries reduce their emission in the future, the total health problem cost associated with NO2 will lower 35% of GDP than in the baseline scenario during the century.
A23A-0764 1340h
Impact of air traffic emissions on airport air quality. Multi-scale modeling, test bed and field measurements
Air traffic emissions are playing a significant role in airport air quality. Engine emissions contribute to the ozone and PM formation. There is an emergence of a need to develop advanced numerical tools and airport emission databases for air pollution studies. Field monitoring at airports necessary to support model assessment is still limited in time and space. The French ONERA AIRPUR project has focused on three objectives: emission inventories; dispersion models; field measurements. Results are presented and discussed in this paper. The ground spatial distribution of LTO emissions using realistic aircraft trajectories, aircraft-engine classification by ICAO, fuel flow methodology and diurnal variations of fleet number, is presented and discussed. Exhaust species time evolution is simulated using a chemical-dispersion model. Results show high emissions of NOx during LTO, and a maximum of CO and Hydrocarbons during taxi. Depending on seasons, the NOx lifetime is varying differently; lower concentration is calculated far away from LTO emissions. Longer-lived pollutants such as ozone are formed downstream and require the use of advanced dispersion models. For this reason, two interactive models coupling the micro and the regional scales are developed and used in this work. A 3D CFD model (CEDRE) simulates the flow characteristics around buildings and the dispersion of emissions. CEDRE boundary conditions are provided by the 3D nested dispersion model MEDIUM/MM5, which includes a surface boundary layer chemistry and calculates the concentration of pollutants from the local to the airport vicinities. The CFD results show a tracer accumulation calculated downstream beside terminals, consistent with observations at some mega-airports. Sensibility studies are conducted to highlight the impact of emissions on ozone formation with MEDIUM. Results show that longer-lived species are produced downstream, their concentration depending on NOx, aromatics and VOC released by engines. Evidence of NOx regime is simulated for the ozone formation at and surrounding airports. At the boarding area, during aircraft parking, APU are generally operated for supplementary electrical power supply for cabin cooling or heating. APU emission indices of NOx, CO, HC and PM equipping civil aircraft are still badly known as they are not certified. Emission indices of soot, NOx, CO, CO2, have been measured on test bed for a specific APU consuming kerosene. Results show that APU emissions are comparable to aero-engine indices for gas, but are far more important for soot. Consequently it is expected that APU emissions are potentially important at airports. Finally, real-time continuous measurements of airborne PM, size distribution and number concentration, have been performed at Nice airport-France, along taxiways for 3 days, in summer 2003 using a 13-stage ELPI. Results show that, when road traffic emissions are not transported into the airport, the observed PM concentration does not exceed the French national threshold for PM mass in summer 2003.
http://www.onera.fr
A23A-0765 1340h
Simultaneous Measurement of NO$_{2}$, NO$_{3}$ and N$_{2}$O$_{5}$ by Cavity Ring-down Spectroscopy During NEAQS-ITCT 2004
We have constructed a cavity ring-down spectrometer (CaRDS) for the simultaneous measurement of nitrogen dioxide, NO$_{2}$, nitrate radical, NO$_{3}$, and dinitrogen pentoxide, N$_{2}$O$_{5}$, in the atmosphere. NO$_{3}$ is known to be the primary nighttime oxidant; during the day, NO$_{3}$ is efficiently destroyed by photolysis. N$_{2}$O$_{5}$ removal is a major pathway for loss of NO$_{x}$, a key ozone production ingredient, from the troposphere. The instrument employs three cavity ring-down cells. In the first cell, NO$_{2}$ is monitored at 532 nm using a frequency-doubled Nd-YAG laser operated in pulsed mode at 100 Hz. In the second channel, the ambient NO$_{3}$ radical concentration is measured at 662 nm, using the output of a dye laser. The third channel is heated to $75\deg$C, which quantitatively converts N$_{2}$O$_{5}$ to NO$_{3}$, and the amount of N$_{2}$O$_{5}$ present is then determined from the increase in the absorption signal at 662 nm. Detection limits are $<1$ pptv for NO$_{3}$ and N$_{2}$O$_{5}$ and 35 pptv for NO$_{2}$ (1 s averages). With this instrument, it becomes possible to continuously characterize all the key nitrogen species involved in NO$_{3}$/N$_{2}$O$_{5}$ chemistry with high precision directly in the atmosphere. The spectrometer was fielded during the NEAQS-ITCT 2004 campaign on board of the research vessel Ron Brown. In this presentation, we compare our CaRDS NO$_{2}$ to that measured using the more traditional method and present some initial findings from this campaign, with particular emphasis on the chemical evolution of NO$_{x}$ species in NO$_{x}$-rich urban plumes in the marine boundary layer.
A23A-0766 1340h
On the Relations Between Transport Patterns and Surface Ozone Variability Over Europe
The analysis presented is based on the data of EMEP ozone measuring network for the period of 1990-1996. To estimate the air transport patterns 4 days back 2D trajectories were used for the same period. They cover the period 1988-1996 and have temporal resolution of 6 hours. Trajectories are calculated by NILU on the basis of EMEP trajectory model and meteorological data provided by the projects EMEP/MSC-W. Analysis of the relation between transport patters and surface ozone concentration are based on the data of 70 European sites (www.emep.int). Transport patters are described by local zonal and meridianal transport indices, calculated for each individual site as the ration of the frequency of arriving from NW, W and SW (NE, N, NW). The following main features of the surface ozone and transport patterns were found: ozone advection with clean marine air in winter in the seaside regions confirmed by high positive correlation coefficients between both the anomalies of zonal and meridianal transport indices and surface ozone concentration; ozone destruction in the polluted regions and in their plumes in winter confirmed by strong negative correlation coefficients between both the anomalies of zonal and meridianal transport indices and surface ozone concentration; ' cleaning of the polluted regions where ozone generation is possible (negative correlations between both the anomalies of zonal and meridianal transport indices and surface ozone concentration) and increase of the correlation with the accumulation of the European pollution; ozone destruction at the North of Europe in summer with the growth of the northern advection. Obtained features of the relations between surface ozone variability and transport patters are used for the estimation of surface ozone regime peculiarity over Europe and for the estimates of the trans-boundary ozone transport.
A23A-0767 1340h
Observations of Ozone in Asian Pollution Plumes in the Free Troposphere at Mt. Bachelor Observatory during Spring 2004
Measurements of trace gases, aerosols and meteorological parameters were made at a new mountaintop site in the Cascade Range of Central Oregon - Mt. Bachelor Observatory (MBO) (44oN, 121oW, 2700 m asl) from February 22 - May 19 2004. One large pollution plume originating from Asia and numerous smaller ones were observed during the campaign. These plumes consisted of enhancements in carbon monoxide (CO up to 300 ppbv), aerosol scattering (ssg up to 50 Mm-1), ozone (O3 up to 80 ppbv), and total gaseous mercury (TGM up to 2.5 ng/m3). For each species we observed much greater enhancements compared to previous observations in the marine boundary layer. In total, 227 hours of measurements (11 distinct events) were classified as significantly influenced by Asian outflow, as indicated by Hysplit kinematic back trajectories that crossed Asia within 10 days, and enhancements in CO and at least one other chemical indicator. These plumes were sampled in the free troposphere and probably not influenced by regional emissions in the Western U.S. since each event was accompanied by descending air and a drop in water vapor. The strongest episode of trans-Pacific transport arrived at MBO on April 25th after only four days of transit. This event produced very strong correlations between all chemical species (r2>0.9) and enhancement ratios that are consistent with an Asian source (e.g. DTGM/DCO). Other ratios can give information on the source characteristics and processing enroute. Some events that were identified as Asian appeared to be mixed with air of stratospheric origin, producing very weak O3/CO correlations. DTGM/DO3 was generally negative during these stratospheric events, which could be the result of gas-phase oxidation of TGM in O3-rich air. Time periods during the spring campaign that were not classified as Asian or stratospherically influenced show very weak relationships between chemical species, reflecting the complex processes that occur during transport. However, the mean CO concentration during the entire period at MBO was 167 ppbv, which is significantly higher than that seen in the marine boundary layer (147 ppbv during same period in 2002), which suggests that Asian emissions have a much greater influence on the background air in the free troposphere compared to the boundary layer. For real-time data at our field sites please the URL below:
http://www.bothell.washington.edu/research/jaffegroup
A23A-0768 1340h
Tropospheric Nitrogen Dioxide Amounts Obtained by GOME Over East Asia in 1996-2002: Validation and Trend Analyses
The Global Ozone Monitoring Experiment (GOME) onboard the European Remote Sensing-2 satellite measured tropospheric nitrogen dioxide (NO$_{2}$) column amounts over East Asia from 1996 through 2002. We compare the GOME data with other independent tropospheric NO$_{2}$ column values at three locations: Moshiri in Japan, Issyk-Kul in Kyrgyzstan, and Zhigansk in Russia. For these locations, stratospheric NO$_{2}$ amounts obtained by satellite-borne solar occultation sensors (SAGE II and HALOE) are subtracted from the total (tropospheric + stratospheric) values obtained by ground-based UV$/$visible spectrometers, yielding estimates of the tropospheric NO$_{2}$ columns at sunrise$/$sunset. The tropospheric NO$_{2}$ column estimates are then corrected for the local time to coincide with the GOME measurements using outputs from a tropospheric chemistry global model. The mean difference between the corrected NO$_{2}$ column estimates and the GOME data is as small as 0.6$\times$10$^{14}$ cm$^{-2}$, with a 1$\sigma$ standard deviation of 6.0$\times$10$^{14}$ cm$^{-2}$. In East Asia, the most significant (exceeding a 3$\sigma$ variation) increasing trends of tropospheric NO$_{2}$ are found only at some locations in eastern China during wintertime. The mean linear trend of the wintertime values in eastern China is estimated to be about 13$\times$10$^{14}$ cm$^{-2}$ year$^{-1}$ (about 8.4% year$^{-1}$) over 1996-2002.
A23A-0769 1340h
Ozone-CO relationships in plumes carrying North American pollution and boreal biomass burning emissions through the central North Atlantic lower free troposphere
North American anthropogenic activities and biomass burning are both significant sources of nitrogen oxides emissions. Recent studies have indicated changes in the NO$_x$\ to CO emission ratio in U.S. urban regions, and amplified response to global climate change in boreal regions is expected to result (and may already have resulted) in increased frequency of large boreal fires. The PICO-NARE mountaintop (2.2~km altitude) station in the Azores Islands is well situated to probe the overall impact of both processes on lower tropospheric O$_3$\ levels. Measurements made there during the summers of 2001--2003 have been analyzed to assess these impacts. The relationship between CO and O$_3$\ in North American pollution outflow was found to be significantly steeper than expected, with a slope ($d[{\rm O}_3]/d[{\rm CO}]$) averaging 1.0 ppbv/ppbv, implying significantly more ozone formation per unit CO emissions than observed in prior measurements over eastern North America and in the nearby downwind region. Potential reasons for this difference, including changes in eastern North American emissions of ozone precursors, airmass history, and NO$_{x,y}$\ export, will be discussed. In contrast to the moderate CO enhancements in North American outflow, we find that boreal fires in Siberia and North America result in the highest CO levels observed, produce ozone enhancements comparable to those in North American pollution outflow, and play a major role in interannual variability of CO. It has been suggested that the magnitude of boreal fires may be increasing as a result of changing boreal climate; these findings imply that such an increase could significantly impact hemispheric scale ozone, CO, and nitrogen oxides levels.
http://www.cee.mtu.edu/~reh/pico
A23A-0770 1340h
Reducing Tropospheric Ozone Through Methane Mitigation: Costs and Benefits
Background ozone concentrations are sensitive to emissions of methane, and climate abatement research suggests that inexpensive methane controls are available. Recent estimates of the sensitivity of ozone to reductions in methane emissions are combined here with estimates of methane control costs and the health and environmental benefits of ozone reductions, to assess the viability of controlling ozone through methane. Identified global cost-saving methane abatement measures will reduce ozone by roughly 0.7 ppb, with reductions that are fairly uniform globally. The global monetized health and agricultural benefits of reducing ozone are estimated to justify reducing $\sim$20% of anthropogenic emissions, without including ozone mortality. Similarly, actions to reduce methane for climate purposes are estimated to have air quality-related ancillary benefits comparable to those of CO2. While methane mitigation reduces ozone more cost-effectively and achieves greater climate benefits than global controls on nitrogen oxides (NOx) and non-methane volatile organic compounds (NMVOCs), methane reduces ozone slowly over a decade, and NOx and NMVOC controls target polluted regions and high-ozone episodes. Increased methane redcutions should be considered alongside NOx and NMVOCs for long-term air quality planning, and because methane reduces ozone internationally, industrialized nations should consider emphasizing methane in the development of unilateral or cooperative climate change or ozone policies.
A23A-0771 1340h
Role of Asian plumes and forest fire smoke on background O3 in the Northeast Pacific/western U.S.
There is some evidence that background ozone in the Northeast Pacific/western U.S. is increasing [Jaffe et al., 2003], however the exact cause for this increase remains unclear. This is especially true given the multiple sources for tropospheric O3 in the region. Using ground or airborne datasets the traditional analysis method is to examine the entire dataset for correlations and relationships. However because of the multiple sources, the correlation of various tracers is often very weak in the entire dataset and important relationships are masked by atmospheric mixing and chemistry. An alternate approach is to segregate the dataset into portions with an identifiable influence from an individual source or group of sources. To do this segregation, we have tried various approaches including trajectories, chemical transport models and some combination of these with the observations. The enhancement ratios of various species (especially CO to ozone) then give specific information on the contribution of that source to the regional ozone budget. To investigate the composition of background O3 and aerosols in the Northeast Pacific/western U.S. our team recently established a new free tropospheric sampling site on the summit of Mt. Bachelor in central Oregon at 2.7 km above sea level. Because of its elevation Asian plumes and stratospheric O3 can be more readily identified. In addition, we have also identified enhancements due to emissions from forest fires in Alaska, Siberia and the western U.S. However even when selecting out one source type, the ratios still have a large deal of variability, likely reflecting variations in emissions and chemical processing during transport. For example, during the spring of 2004, we identified numerous episodes of enhanced CO, ozone, aerosols and elemental mercury associated with sources in Eurasia. During these episodes, we measured enhancement ratios for ozone to CO and mercury to CO of 0.18 +/- 0.20 ppbv/ppbv and 0.0037 +/- .0031 ng/m3/ppbv (n=10), respectively. By comparison, plumes from biomass burning emissions have much higher aerosol/CO enhancement ratios and lower Hg/CO ratios. Based on a comparison of this enhancement ratio with the source ratios, we propose that the Hg/CO ratio is our most specific indicator of the degree of Asian influence on background air in the western U.S.
A23A-0772 1340h
Identification of free tropospheric air masses at the new Mt. Bachelor, Oregon observatory
In February 2004, we established a new atmospheric observatory on the summit of Mt. Bachelor, Oregon in order to better understand the long range transport of chemicals and anthropogenic pollutants to North America. Previous work on the inflow to the Pacific Northwest (Weiss-Penzias 2004, 2003, Jaffe 2003) has been able to identify Asian influence on a costal site, but aircraft observations (Price et al. 2003, Kotchenruther et al 2001) and modeling work (Jaegle et al. 2003) have shown that transport events are much more frequent in the free troposphere. The detection of these pollution plumes in the planetary boundary layer is greatly complicated by the turbulent meteorology and complex chemistry of the boundary layer. The Mt. Bachelor Observatory (MBO) ( 2.7 km a.s.l.) was established to allow for continuous sampling at a site that likely experiences free tropospheric air a majority of the time. In order to help understand the influence of the boundary layer on the spring 2004 MBO observations, we have conducted a meteorological analysis for this period using several measured and modeled parameters. Our initial analysis of virtual soundings generated by the mesoscale NWP model, MM5 (University of Washington, Seattle), and of measured water vapor content, indicate that during the spring campaign (Mar-May), on at least 50% of the days, the daytime mixed layer height did not reach MBO before beginning to collapse at sunset into a shallow night time boundary layer. Thus, for the spring of 2004, we conclude that MBO experienced free-tropospheric air for more than 50% of the time; however, this is likely a lower limit. An objective analysis of water vapor and wind measurements with the goal of further improving the diagnosis of boundary layer influence will be presented along with their application to several long-range transport episodes at MBO. Additional measurements to be made at the site will hopefully allow us to make a more accurate assessment of the boundary layer height and its influence on the MBO observations. (See presentation by Weiss-Penzias et al., for a discussion of the chemical observations during this same time period.)
A23A-0773 1340h
Weekday/Weekend Differences in Ambient Concentrations of Primary and Secondary Air Pollutants
We evaluated the differences between mean day-of-week ambient concentrations of ozone precursors, ozone, and other secondary species using 1998-2003 ambient air-pollutant data from monitoring sites in 23 states in New England, the Midwest, the mid-Atlantic, and isolated urban areas in the western and southern U.S. For CO, NO, and NOx, we examined different times and averaging intervals: hourly (6 am and noon), three-hour averages (6-9 am, 9 am-12 noon, 12 noon-3 pm), and nine-hour daytime averages (6 am-3 pm). The median decreases at 6 am and noon bracketed the median daytime (6 am to 3 pm) decreases and closely represented the decreases occurring for the 3-hour averaging times 6 am-9 am and 12 noon-3 pm. In all areas and at both 6 am and noon, substantial declines in ambient concentrations of NO, NO2, and NOx occurred on weekends. Relative to Wednesdays, the median declines in 6 am Sunday ambient NO and NOx levels were 70.6 percent (interquartile [IQ] range 60.3-77.9 percent) and 57.5 percent (IQ range 47.2-63.4 percent), respectively; the median declines of 6 am Saturday NO and NOx levels were 52.7 percent (IQ range 40.8 to 61.8) and 40.1 percent (IQ range 33.0 to 48.1), respectively (204 sites with NO, NO2, and/or NOx). Most decreases were statistically significant (e.g., 173 NO sites, 170 with lower 6 am concentrations on Sundays than on Wednesdays, 153 statistically significant [p$<$0.01] decreases). The median decreases in ambient CO concentrations were smaller than those for NO and NOx. Relative to Wednesdays, the median declines in 6 am ambient CO levels at 227 monitors were 41.5 percent (IQ range 30.6 to 53.0) on Sundays and 28.1 percent (IQ range 20.7 to 36.6) on Saturdays. Most decreases were statistically significant (e.g., 227 sites, 220 with lower 6 am concentrations on Sundays than on Wednesdays, 202 statistically significant [p$<$0.01] decreases). For PAMS hydrocarbon data, day-of-week means were determined for the 9 am-3 pm ambient concentrations of alkanes, alkenes, aromatics, sums of species, and selected compounds. The median Wednesday-Sunday decreases in daytime concentrations of aromatics ranged from 12.4 percent (Baltimore) to 49 percent (Dallas-Fort Worth); the median of the median decreases was 29.7 percent. The median decreases in the sum-of-species ranged from 6.1 to 26.2 percent. For ozone, we determined day-of-week averages for both peak 1-hour and peak 8-hour concentrations. Each peak ozone average was computed in three ways: (1) using all measurements from the months of March through October of each year, (2) using the top three peak ozone days for each day of the week and each year, and (3) using the top ten peak ozone days for each day of the week and each year. Over all 480 ozone monitoring sites, the largest number of weekend ozone increases occurred for peak 8-hour concentrations determined from all monitoring days: these peak ozone levels were 3.4 percent higher (median change) on Sundays than on Wednesdays (IQ range 0.4 to 6.9 percent higher on Sundays; 294 weekend increases, 186 weekend decreases, 8 decreases statistically significant). The largest number of weekend ozone decreases occurred for the peak 1-hour concentrations determined from high-ozone days: median 2 percent lower on Sundays than on Wednesdays (IQ range 2.7 percent Sunday increase to 6.3 percent Sunday decrease; 226 increases, 254 decreases, 22 decreases statistically significant). The relative lack of change in ozone concentrations on weekends, despite the occurrence of substantial and widespread weekend decreases in ambient precursor concentrations, merits further study.
A23A-0774 1340h
Vertical Profiles of Nocturnal O$_3$-NO$_x$ Chemistry in the Urban Boundary Layer --- Field Observations in Phoenix and the Corresponding Model Studies
Nocturnal boundary layer (NBL) chemistry in urban areas is strongly influenced by surface NO$_{x}$ emissions. Vertical mixing in combination with chemical transformations leads to distinctive vertical profiles of reactive trace gases. The O$_{3}$-NO$_{x}$ chemistry system, therefore, varies with altitude in the stable NBL. To understand the influence of vertical mixing on nocturnal chemistry and to improve the accuracy of urban air pollution models, vertical distributions of a number of trace gases were measured in the lowest 10-140 m of the atmosphere with a long-path DOAS instrument in downtown Phoenix, AZ in June-July, 2001. Here we present and analyze results from these measurements. Strong positive vertical profiles of O$_{3}$ and NO$_{3}$ and negative vertical profiles of NO$_{2}$, HONO, HCHO and SO$_{2}$ were observed during all nights. The magnitudes of gradients were significantly larger than earlier observations in rural or suburban areas due to higher nighttime ground-level emissions. Vertical profiles of O$_{x}$ (O$_{3}$ + NO$_{2}$) were much lower than those of O$_{3}$ and NO$_{2}$. This shows the dominant role of the reaction of NO with O$_{3}$ in the urban NBL. In all cases, total O$_{x}$ levels decreased gradually throughout the night. An analysis of the NO$_{3}$ production rate reveals complex vertical profiles of this parameter depending on the distribution of both NO$_{2}$ and O$_{3}$. The positive NO$_{3}$ profiles are, however, a consequence of strong emissions of NO and VOCs near the surface. The calculated steady-state N$_{2}$O$_{5}$ distribution further implies vertical variations in the atmospheric loss of O$_{x}$ and NO$_{x}$. To quantitatively analyze our observations, we employed a 1-D chemical transport model. The model results generally agree with the observations. Our calculations reveal that the profiles of O$_{x}$ are controlled by the interplay between, NO$_{x}$ emissions, dry deposition of O$_{3}$, and the initial O$_{3}$ level. NO$_{3}$ and N$_{2}$O$_{5}$ chemistry was found to be responsible for a large part of the ultimate O$_{3}$ and NO$_{x}$ loss at night. Details of the model results will be discussed.
A23A-0775 1340h
Quantifying Source-Receptor Relationships between NOx Emissions and O3 Concentrations in Downwind States in the Continental U.S
The objective of this study is to examine source-receptor relationships between NOx emissions from individual U.S. states and the O3 that is produced from that NOx and transported to downwind states. US EPA Models-3/CMAQ is used to calculate ambient concentrations of chemical species by using emissions from MCNC SMOKE and meteorology from NCAR/PSU MM5 as input, and simulating chemical transformation, transport, and deposition processes that determine the fate of tropospheric O3. We first evaluate the ability of CMAQ to capture the main features of surface O3 and its variations over the continental United States by comparing model output with hourly O3 measurements obtained from AIRS and CASTNet surface measurements. Next, we present a process budget analysis of O3 to determine the relative magnitudes of local photochemistry and remote transport to each receptor state. Finally, we present the source-receptor relationship between O3 and NOx emissions from individual states in a summer month (July 1996). We conclude by quantifying both where the O3 produced by a fixed quantity of NOx emissions from each source state goes, and from which states the O3 each receptor state receives comes from.
A23A-0776 1340h
What PAN Tells us About Continental C & N Outlflow, Airmass Chemical Reactivity, and Appropriate Simulation
We compare two recently improved simulations of carbon and nitrogen outflow from North America to a spatially extensive set of airborne observations made in September, 1997, NOAA's North Atlantic Regional Experiment, NARE-97. Peroxyacetyly nitrated, PAN is our central focus. PAN production has strong analogies to pollutant O$_3$ formation in the lower troposphere; it also helps control remote NO$_x$ concentrations. PAN will be analyzed in two ways: (a) as a measure of continuing organic-associated radical activity in distant continental outflow plumes, and (b) as a check on resolution effects in large-scale models. One simulation, NASA's Global Modeling Initiative tropospheric model, currently at 4$^\circ$x4$^\circ$ resolution, will have its first event-simulation tests reported here. The other, the University of North Carolina's research version of the Community Multiscale Air Quality Model, receives here some first tests for very long-distance transport. This model has \sim 1$^\circ$x1$^\circ$ resolution, but is limited to the region from the Rockies to the Central Atlantic Ocean. Since PAN production is proportional to [acetyl peroxy] x [NO$_2$], and each of these factors is expected to decrease rapidly in plumes, PAN provides an incisive analysis tool regarding the effect of resolution and correct meteorology. The competition between reaction and lofting to cooler temperatures is key to PAN concentrations and the global reach of pollutant NO$_x$. An early science result seems signficant: analysis of PAN and the PAN/NO$_2$ ratio in appropriate regions suggest that currently simulated concentrations of CH$_3$CHO seem to be consistent chemically with measured and modeled organics. Current kinetics does appear consistent with than the much higher values of acetaldhyde measured by Hanwant Singh et al. in the Pacific and the Atlantic (but during other missions). We will explore the implications of our comparisons regarding the fate of NO$_x$ and organics, the variable production of O$_3$ in extended continental plumes.
http://geo.arc.nasa.gov/sgg/chatfield/presentations.html
A23A-0777 1340h
Lightning NO$_{X}$ Production and Ozone Photochemistry in the July 10 1996 STERAO Storm Studied with a 3-D Coupled Cloud/Chemistry Model
On July 10 1996, the development of a multicellular storm was observed during the Stratospheric-Tropospheric Experiment: Radiation, Aerosols and Ozone (STERAO) field campaign. During the storm, cloud-to-ground lightning flashrates were available from the National Lightning Detection Network, and total lightning activity was observed by the ONERA interferometer. The 3-D Goddard Cumulus Ensemble (GCE) cloud resolving model and an accompanying cloud scale chemical transport model (CSCTM) were used to simulate the evolution and chemical environment of the observed thunderstorm. Estimates of NO$_{X}$ production per lightning flash and per meter of lightning flash channel were obtained by comparing in situ chemical observations taken in the thunderstorm anvil with model results. The effect of lightning produced NO$_{X}$ on ozone was analyzed by comparing a simulation including lightning NO$_{X}$ production with a simulation which did not include a source of lightning NO$_{X}$. In order to estimate the effects of lightning NO$_{X}$ on downstream ozone production in the 24 hours following the convection, a chemistry-only version of the CSCTM was employed.