A51D-0725
Los Angeles Heat Waves Are They Becoming More Frequent and Longer in Duration?
Los Angeles is experiencing more heat waves, an event defined by 3 consecutive days above 32.2 C (90 F) in Los Angeles, and also more extreme heat days, defined as days above 32.2 C (90 F). These numbers have increased by 1.72 C (3.09 F) per century and 22.8 per century occurrences, respectively. Both have more than tripled over the last 100 years as a consequence of the steady warming of Los Angeles. We looked at daily maximum and minimum temperatures from 1906-2006 from the Department of Water & Power (DWP) downtown station. The average annual maximum temperature in Los Angeles has warmed by 2.8 C (5.0 F) per century. Also the average annual minimum temperature is steadily warming at 2.3 C (4.2 F) per century. By season, the greatest rate of change was during the summer months for both maximum and minimum temperature, with late fall and early winter having the least rates of change. Furthermore, along with the increase in heat waves there was an increase in heat wave duration. Heat waves lasting longer than six days occurred regularly after the 1970s but were non-existent from the start of 1906 to 9/24/1956 when the first 6-day heat wave was recorded. There are two 13-day long heat waves later in the record on August 12, 1983 and August 29, 1995, while 1997 had the highest number of heat wave events (7) and 1983 and 1997 had the most extreme heat days. Both years were El Niño years. While heat days have increased dramatically in the last century, extreme cold days, where minimum temperature is below 7.2 C (45 F), shows a slight decreasing trend. This is expected since the overall minimum temperatures are increasing. The summer of 2006 experienced an unusually high number of deaths due to extreme heat events in California. Abnormally high sea surface temperatures off the southern California coast and an influx of monsoonal moisture combined with record heat creating dangerous conditions. The trends in Los Angeles' heat waves indicate that the summer of 2006 may not be a singular event, but possibly more common in the future.
A51D-0726
Predicted Impacts of Future Climate Change and Land-Use Change on Surface Ozone in the Houston Area
We investigated the impacts of climate and land-use change on regional climate and surface ozone under the future IPCC A1B scenario in the greater Houston area. We applied the Weather Research and Forecasting (WRF) model with chemistry (WRF-CHEM) to the Houston area for current and future years. The high-resolution initial and boundary meteorological conditions for the WRF-CHEM model were obtained by running the WRF model at 12-km grid spacing driven by 6-hourly Community Climate System Model (CCSM) version 3 outputs. High- resolution land-use data from National Land Cover Dataset (NLCD) was used in the WRF-CHEM model coupled with an Urban Canopy Model (UCM). For future-year simulations, we implemented a detailed future urban land- use data based on projected population growth to investigate the effects of future land-use change on regional climate and ozone concentration. For the urban area, our simulation results indicate that the effect of climate change accounts for an increase of 2.6 ppb in daily maximum 8-hr ozone concentration and land-use change exerts more influence than climate change. The combined effect of climate change and land-use change can be up to 6.2 ppb. Predicted distribution of the number of extreme ozone days with the daily maximum 8-hr ozone concentration larger than 84 ppb is similar to the pattern of increases in ozone concentration. The increase in extreme ozone days can be up to 4-5 days in August in which land-use contributes to 2-3 days increase. We also find climate change and land-use change have different impacts in different regions. Additional sensitivity experiments on the impacts of anthropogenic emissions show that the impacts of future change in anthropogenic emissions are comparable with the effects of land-use change on ozone concentration.
A51D-0727
Using Beryllium-7 to Assess Cross-Tropopause Transport in Global Models
The stratosphere-troposphere exchange (STE) flux of ozone plays an important role in the tropospheric ozone budget. Representing this flux in global models is critical to quantitatively understanding the tropospheric ozone budget. Beryllium-7 (7Be), produced cosmogenically in the stratosphere and upper troposphere, has long been used to determine the stratospheric origin of tropospheric air. Here we use the Global Modeling Initiative (GMI) modeling framework to assess the utility of 7Be for evaluating STE in global models. The GMI chemistry and transport model (CTM) was used to simulate atmospheric 7Be distributions using four different meteorological data sets, featuring significantly different STE characteristics. The data sets were generated by the Goddard Space Flight Center Global Modeling and Assimilation Office (GMAO) GEOS-STRAT assimilation, the Goddard Institute for Space Studies GISS II' general circulation model (GISS II' GCM), the GMAO finite-volume GCM (fvGCM), and the GMAO GEOS-4 data assimilation system (GEOS-4 DAS). The simulations were compared with observed 7Be concentrations at the surface and in the upper troposphere / lower stratosphere (UT/LS), as well as surface deposition fluxes. The UT/LS observations are climatologies constructed from ~25 years of aircraft and balloon data from the US Environmental Measurements Laboratory RANDAB database. All simulations capture the observations at 12-16km, but underestimate concentrations at higher altitudes, especially at Northern Hemisphere middle/high latitudes with GEOS-STRAT. Comparison of the surface fraction of air of stratospheric origin estimated from the 7Be simulations with observationally-derived estimates indicates excessive cross-tropopause transport at middle latitudes in simulations using GEOS-STRAT and at high latitudes using GISS II' meteorological data. These simulations also overestimate 7Be deposition flux at middle latitudes (GEOS-STRAT) and at high latitudes (GISS II'). We conclude that 7Be concentrations and deposition fluxes may be used routinely to assess cross- tropopause transport in global models. The relationship between the STE fluxes of 7Be and ozone will also be discussed. http://research.nianet.org/~hyl
A51D-0728
Preliminary results of the Cloud-Aerosol Interaction Measurements (CLAIM) 2007 campaign on the Amazon Basin, Brazil
Clouds and precipitation play an important role on Earth's radiation budget, water and hydrological cycles, as well as energy cycles through latent heat release in the atmosphere. Under several aspects the interaction between aerosols and clouds is still a poorly understood process, and one reason for this is the lack of experimental observations to characterize the evolution of cloud microphysical structure. An instrumentation suite was put together to assess these issues. The Cloud Scanner is a scanning radiometer composed of 2 wavelengths in the near infrared (2.10 and 2.25 μm) used for the separation between ice and water, and 3 wavelengths in the thermal infrared (8, 11 and 12 μm) for the measurement of cloud brightness temperature, cirrus properties and water vapor correction. The Rainbow Camera is a multiangle imaging polarimeter with the wavelengths 0.47, 0.55, 0.66, 0.76, 0.87, and 0.91 μm, with 60 degrees FOV, used to retrieve droplet effective radii and distribution width. Both instruments were integrated onto a research aircraft for a field campaign over the Brazilian Amazon Basin from Sep-Oct 2007 under varying conditions of aerosol loading and cloud type, development stages, and cover area. The preliminary results obtained include real-time mappings of ice/water separation for clouds, with temperature profiles allowing for the retrieval of glaciation levels for a variety of cloud developmental stages and aerosol loadings, including deep convective cumulus clouds and/or high aerosol content. Vertical profiles of effective radius can be obtained using the measurements in 2.10 μm as entries in a look up table from a 3D radiative transfer model for the cloud field. The post-processed polarimeter measurements allow retrieving a polarized reflectance signal from which one can derive effective radii and distribution widths of droplets for clouds in the observed scenes. These results help understanding and quantifying the effects of cloud-aerosol interactions and their consequences for cloud microphysics.
A51D-0730
Quantification of Wood Smoke Markers in Fine Atmospheric PM in the New York City Airshed
Seasonal emissions from residential wood combustion, natural wildfires, agricultural burning and solid waste combustion are considered to be major sources of fine particles to the NYC metropolitan airshed. Wood smoke produced from the combustion of cellulosic material consists of polar organic compounds which are highly water-soluble. As alternative forms of energy production including biofuels for residential heating are developed and become more widely used, a key science question is how much of the carbonaceous PM2.5 currently is from wood smoke in urbanized areas and to what extent is this influencing atmospheric chemical properties. This project focuses on the quantitation of polar organic compounds extracted from fine particle samples (PM2.5) collected as part of the Speciation of Organics for Apportionment of PM-2.5 in the New York City Area (SOAP). The SOAP network operated from May 2002 to May 2003 at four sites: Queens, NYC (high density urban residential); Elizabeth, NJ (adjacent to the NJ Turnpike); Westport, CT (downwind NYC residential); and a regional background site in Chester, NJ (upwind NYC). A quantitative extraction and gas chromatographic/mass spectrometric (GC/MS) chemical analysis procedure was developed and evaluated. Trimethylsilyl (TMS) derivatives were prepared prior to GC/MS analysis and 5-point calibrations and multiple replicates were evaluated to ensure method precision. Levoglucosan was used as the primary marker for cellulose combustion; however a suite of monosaccharides and disaccharides and dehydroabietic acid, a marker indicative of soft wood combustion, also were quantified. Levoglucosan was found during each season at all four sampling locations with ambient mass concentrations ranging from 2.36 ng/m3 to 189 ng/m3. These values represent an estimated low of 0.73 percent to a high of 69 percent of organic carbon in the fine PM from wood smoke. The lowest levoglucosan concentrations were present consistently at the Chester, NJ upwind site and the highest were seen most frequently in Westport, CT, a predominantly residential area. Levoglucosan concentrations were lowest in spring and highest during late fall, early winter, or late winter. The results from the remaining sugar marker compounds showed no persistent trends spatially or seasonally. Dehydroabietic acid also was found in the fine PM with similar trends to levoglucosan; the concentrations ranging from a low of 1.6 ng/m3 (Westport, spring) to a high of 98 ng/m3 (Elizabeth, early spring). These results for metropolitan NYC indicate that wood smoke is currently a major component of PM mass and is prevalent year round and is derived from a combination of seasonally variable sources.
A51D-0731
Constraining the budget of DMS in the remote marine boundary layer - results from the Pacific Atmospheric Sulfur Experiment (PASE)
The Pacific Atmosphere Sulfur Experiment (PASE) investigated the chemistry of sulfur in the remote, unpolluted marine boundary layer of the equatorial Pacific. The experiment was conducted in the vicinity of Christmas Island (2N, 157W) using the NCAR C-130 aircraft. High rate (25 Hz) measurements of DMS, SO2 and wind speeds were made along with low rate measurements of OH, HO2, aerosol size spectra, and other species. The flights were typically flown at altitudes corresponding to the surface layer, middle and top of the boundary layer, as well as the buffer layer above (where most of the trade wind cumulus resided). Horizontal and vertical fluxes were measured to constrain the scalar budgets of DMS and SO2. Preliminary results suggest a large and persistent sink of DMS in addition to reaction with OH. Reactions of DMS with BrO and Cl are considered as potential candidates with concentrations estimated from bromine and chlorine depletion in sampled sea salt particles.
A51D-0732
DMS Air-Sea Transfer Velocity Functionality From DOGEE
We measured the sea/air flux of DMS by eddy correlation (EC) on an sub-hourly time scale in the North Atlantic from the UK ship RRS Discovery in June and July of 2007, as a part of the Deep Ocean Gas Exchange Experiment, DOGEE. We used an atmospheric pressure ionization mass spectrometer (APIMS) with an internal isotopically-labeled standard (D3-DMS) to rapidly measure atmospheric DMS. We also measured seawater DMS concentrations with a purge and trap system on a roughly seven-minute time scale, so that we could compute the DMS transfer velocity (Vt, the EC-derived flux divided by the interfacial concentration difference) on an hourly basis. Wind speeds ranged from nearly calm to over 15 m/s. We compare our exchange velocities with simultaneous measurements of wave slope, bubbles, surfactants (intentional patches), and exchange velocities from dual-tracer releases. The time-scale (hourly) of the sea/air gas fluxes and exchange velocities enables us to address the functionalities of the other controlling factors.
A51D-0733
Comparison of CMAM Simulations of Carbon Monoxide (CO), Nitrous Oxygen (N2O), and Methane (CH4) With Observations From Odin/SMR, ACE-FTS, and AURA MLS
Simulations of CO, N2O and CH4 from a coupled chemistry-climate model (CMAM) are compared with satellite measurements from ACE-FTS, Odin/SMR and AURA MLS. Pressure-latitude cross-sections and seasonal time series demonstrate that CMAM reproduces the observed global distributions and follow the polar evolutions seen in the CO, N2O, and CH4 measurements. Generally, excellent agreements are found in CO monthly zonal mean profiles in the stratosphere and mesosphere for various latitudes and seasons. The difference between the simulations and the observations are generally within 50%. Comparisons of N2O show that CMAM follows the measurements very well, usually within 15% of the relative difference, in the lower and middle stratosphere but has negative bias with factors as small as 0.1 in the upper stratosphere. The CMAM CH4 profiles also follow the observations as the N2O, but have negative biases in the upper stratosphere too. These negative biases are probably due to a transport problem from the lower stratosphere to the upper stratosphere. CO measurements from 2004 and 2006 by SMR and MLS show evidence of descent of air from the mesosphere into the stratosphere in the Arctic after strong stratospheric sudden warmings. CMAM also captures this feature. We will also show the "tape recorder" and the Quasi-Biennial Oscillation (QBO) signal from the SMR N2O observations. CMAM can produce the "tape recorder" signals with CO and N2O but cannot produce the QBO signals. Nevertheless, this study confirms that CMAM has an overall good capability to simulate middle atmospheric transport processes besides identifying its deficiencies.
A51D-0734
Analysis and Comparison of the Vertical Disribution of Ozone from Satellite, Sondes and Ground-based FTS in Northern Greenland
Part of the Arctic Station for the Network for the Detection of Stratospheric Composition Change (NDACC) consists of O3 sondes and the mid-IR high resolution solar viewing Fourier transform spectrometer (FTS) at Thule, Greenland (76.5N, 68.8W, 225masl). The FTS operates autonomously providing observations on 75 days per annum on average. O3 profile retrievals using the optimal estimation (OE) technique from the FTS spectra have a typical degrees of freedom for signal (DOFS) of about 4.2. Column and vertical profiles of O3 are compared between the FTS and sondes on days of coincident measurement. These ground-based O3 measurements are then compared with data from the OMI, TES, MLS and HIRDLS sounders on AURA and the ACE FTS aboard SCISAT-1.
A51D-0735
TES observations of tropospheric ozone as a greenhouse gas
We present satellite observations of the downward radiative flux from tropospheric ozone, for cloud free ocean conditions. This analysis uses infrared (IR) radiance spectra, integrated over the 9.6 micron ozone band between 985 to 1080 cm-1, and ozone profile retrievals from the Tropospheric Emission Spectrometer (TES) on EOS-Aura. We examine the sensitivity of the outgoing longwave radiation (OLR) in the 9.6 micron band to upper tropospheric ozone and water vapor by separating the data into hemispherical and sea-surface temperature (SST) ranges. For 2006 data, we estimate an annual average downward flux for upper tropospheric ozone of 0.48 ± 0.13 W/m2 with a standard deviation of 0.24 W/m2 for the latitude range between 45°S to 45°N. This estimate includes natural and anthropogenic ozone sources and is higher than the 2007 IPCC average for climate model estimates of anthropogenic tropospheric ozone radiative forcing of 0.35 W/m2. We also observe that water vapor dominates the clear-sky ocean variability of the outgoing IR radiation in the 9.6 micron ozone band for SSTs higher than 299 K, consistent with the "super greenhouse effect". This underscores the importance of chemistry-climate coupling in forcing predictions for tropospheric ozone.
A51D-0736
Evaluation of OMI Column Retrievals of HCHO, BrO and OClO Using Ground-Based DOAS and FTS Measurements, SCIAMACHY and GOME Satellite Observations, and GEOS-Chem Modeling
We present comparisons of the operational column retrievals of OMI BrO, OClO, and HCHO from the Dutch- Finnish Ozone Monitoring Instrument (OMI) on EOS/Aura with space-based observations from SCIAMACHY (all molecules) and GOME (BrO and HCHO), ground-based MAX-DOAS and FTS observations of BrO and HCHO, and GEOS-Chem modeling results for HCHO. Current operational retrievals of BrO, OClO, and HCHO from OMI suffer from across-track "striped" spatial structures, arising predominantly from insufficient dark current corrections in the radiance and irradiance spectra. Driven by the need to avoid the most affected regions of the CCD detector, sub-optimum retrieval windows had to be chosen. In the case of HCHO and BrO this contributed to the current 35-40% underestimate in derived columns compared with correlative ground-based and satellite data, and to OClO columns that are a factor of two too high compared with SCIAMACHY columns. Recent improvements in the OMI radiances and irradiances, particularly the implementation of daily dark current updates, greatly reduce the across-track striping in the retrieved column amounts of all molecules considered here. We also show that better optimization of spectral fitting windows and the implementation of soft calibration in the retrieval algorithms greatly improves the BrO, OClO, and HCHO data products. These improvements lead to better agreement between columns from OMI and other instruments. We present daily and monthly comparisons between OMI and selected ground-based stations, global comparisons of BrO and HCHO of OMI, GOME and SCIAMACHY, and regional comparisons with results from the GEOS-Chem model.
A51D-0737
Atmospheric Chemistry of Fluorinated Ethers: Estimation of Radiative Forcing from Chemical Structure
Fluorinated compounds absorb within the atmospheric window and contribute approximately 13% of the radiative forcing (RF) of climate change associated with long-lived greenhouse gases. Among the halocarbons with the highest RFs are fluorinated ethers, which are increasingly being used as replacements for ozone depleting substances. Radiative forcing by fluorinated ethers is not simply proportional to the number of C-F bonds contained in the molecule. It has been proposed that changes in the chemical environment of the C-F bond can change the radiative properties of the bond. For instance, increasing fluorination increases the bond strength, moving the absorption out of the atmospheric window. Density functional theory was employed to calculate the infrared spectra of a series of fluorinated ethers and to estimate the radiative forcing contribution of different substituent groups. Values and trends were consistent between theoretically and experimentally derived radiative forcing values. A structure-activity relationship was developed to estimate radiative forcing from chemical structure. This relationship avoids the time and expense associated with chemical synthesis and laboratory experiments and may be a useful screening tool to search for compounds with lower radiative forcing values.
A51D-0738
Heterogeneous Photochemical Oxidation of Sulfur Dioxide
The gas phase oxidation of sulfur dioxide by the hydroxyl radical is a significant source of sulfate aerosol in the troposphere and stratosphere. Stockwell and Calvert (1983) performed fifteen chamber experiments where mixtures of HONO, NO, NO2, H2O, SO2 and CO were photolyzed in synthetic air or in nitrogen containing approximately 50 ppm oxygen. They found that the atmospheric oxidation of SO2 by hydroxyl radical was a chain process that occurs through the production of an HO2 radical followed by reaction with NO to reproduce HO. We have reanalyzed this dataset and we have found that a very large amount of the observed SO2 oxidation (70.0 ± 9.1 %) is not explained through the HO + SO2 reaction alone. The Regional Atmospheric Chemistry Mechanism (RACM2) was used to investigate additional chemical pathways for the oxidation of SO2. A mechanism consisting of photochemical heterogeneous reactions is proposed to account for the observed additional sulfur dioxide oxidation not accounted for by gas phase oxidation. The analysis showed that the measured time dependent SO2, CO2 and nitrogenous compound concentrations could be simulated by the photochemical heterogeneous mechanism in conjunction with the RACM2 mechanism.
A51D-0739
Photoprocessing of Pyruvic Acid in the Earth's Atmosphere
Pyruvic acid is a ketoacid produced in the atmosphere from biogenically emitted organic compounds through photochemical oxidation. It has been observed in the gas-phase, in collected aerosols, and in rainwater. Furthermore, it has been measured in continental and marine atmospheres. Pyruvic acid, as well as other ketoacids, is known to be a good nucleating agent for aerosols and clouds. We propose a new mechanism for the photoprocessing of pyruvic acid. Using visible light to promote the molecule into a vibrational overtone of the OH stretch, the molecule possesses enough energy to surmount the barrier for a unimolecular reaction. This reaction is facilitated by the hydrogen bond present in the stable conformer of the molecule. The process involves excitation by red photons of the OH stretching vibrational manifold of the ground electronic state at energies sufficiently high to exceed the transition state for reaction. The early time dynamics for photodecarboxylation of pyruvic acid has been studied spectroscopically by analysis of frequencies, intensities, and bandwidths of the OH stretching vibrational overtone transitions. As evidence of this reaction we have data showing early time dynamics using cavity ring-down spectroscopy to illustrate the lifetimes of these overtones. Additionally, we have photochemical data of increased carbon dioxide produced upon photolysis with low energy photons. Sunlight initiated chemistry by excitation of OH vibrational overtones of organic acids may contribute to the atmospheric processing of hydrophilic compounds. The chemistry is expected to affect aerosol processing and cloud nucleation.
A51D-0740
The Impact of Cloud Correction on the Redistribution of Reactive Nitrogen Species
Clouds are particularly important to air quality. Yet, correct prediction of clouds in time and space remains to be a great challenge for the air quality models. One aspect of cloud impact on air quality is the modification of photolysis reaction rates by clouds. Clouds can significantly alter the solar radiation in the wavelengths affecting the photolysis rates. Such modifications significantly impact atmospheric photochemistry and alter the chemical composition of the boundary layer. It also alters the partitioning of chemical compounds by creating a new equilibrium state. Since air quality models are often being used for air quality and emission reduction assessment, understanding the uncertainty caused by inaccurate cloud prediction is imperative. In this study we investigate the radiative impact of clouds in altering the partitioning of nitrogen species in the emission source regions. Such alterations affect the local nitrogen budget and thereby alter the atmospheric composition within the boundary layer. The results from two model simulations, one in which the model predicted clouds are used (control), and the other in which the satellite observed clouds have been assimilated in the model were analyzed. We use satellite retrieved cloud transmissivity, cloud top height, and observed cloud fraction to correct photolysis rates for cloud cover in the Community Multiscale Air Quality (CMAQ) modeling system. The simulations were performed at 4- and 12-km resolution domains over Texas, extending east to Mississippi, for the period of August 24 to August 31, 2000. The results clearly indicate that not using the cloud observations in the model can drastically alter the predicted atmospheric chemical composition within the boundary layer and exaggerate or under-predict the ozone concentrations. Cloud impact is acute and more pronounced over the emission source regions and can lead to drastic errors in the model predictions of ozone and its precursors. Clouds also increased the lifetime of ozone precursors leading to their transport out of the source regions and caused further ozone production downwind. The longer lifetimes for NOx and its transport over regions high in biogenic hydrocarbon emissions (in the eastern part of the domain) led to increased ozone production that was missing in the control simulation. An indirect impact of the clouds in the emission source areas is the alteration in partitioning of nitrogen oxides and the impact on nitrogen budget due to surface removal. This is caused by the disparity between the deposition velocity of NOx and the nitrates that are produced from oxidation of NOx. Under clear skies, NOx undergoes a chemical transformation and produces nitrates such as HNO3 and PAN. In the presence of thick clouds, due to the reduction in the photochemical activities, nitrogen monoxide (NO) rapidly consumes ozone (O3) and produces nitrogen dioxide (NO2) while the production of HNO3 and loss of NOx due to chemical transformation is reduced. Therefore, in one case there is more loss of nitrogen in the vicinity of emission sources. A detailed analysis of two emission source regions, Houston-Galveston and New Orleans area, will be presented. Acknowledgments. This work was accomplished under partial support from Cooperative Agreement between the University of Alabama in Huntsville and the Minerals Management Service on the Gulf of Mexico Issues.
A51D-0741
Effects of Relative Humidity and Carbon Monoxide on the ozone-initiated Reaction of Gaseous Mercury: Kinetic & product studies
Ozone is assumed to be the predominant tropospheric oxidant of (Hg0(g)), defining mercury global atmospheric lifetime. In this study, for the first time, we have examined the effect of H2O(g) and CO(g) on the bi-molecular O3-initiated oxidation of rate of Hg0(g), knet, at 296K. Kinetics of these reactions were studied as absolute rates using gas chromatography coupled to mass spectrometry (GC-MS) at different concentration regimes, surface-to-volume ratios, and wall treatments. We observed a maximum 170% increase in the rate constant at 60% RH in a 1L flask, and smaller increases at other humidities, in larger flask volumes the significance of RH decreased in contrast with the experiments where CO was used as the third body. Product studies were performed using mass spectrometry and high resolution transmission electron microscopy coupled to an electron dispersive spectrometer (HRTEM-EDS). Our results give evidence for enhanced chain growth of HgO(s) on a carbon grid at RH = 50%. The atmospheric implications of our findings will be discussed.
A51D-0742
Latitudinal Patterns of N2O Concentration Variations Over The Northern And Western Pacific For 1992-2006
Atmospheric N2O concentration over the Pacific have been observed by Tohoku university, using commercial ships sailing between Japan and North America and between Japan and Australia or New Zealand since 1991. The N2O concentration showed secular increasing trend and interannual variation at all sampling positions in the Pacific observation, while the seasonal cycle was detected only at northern high latitudes. Longitudinal distributions of the annual mean N2O concentration over the northern pacific were almost flat within 0.2 ppbv, reflecting the atmosphere well-mixed by the westerly and longitudinally even distribution of N2O sources around the northern Pacific. The latitudinal distribution showed clear north- south gradient, in which the northern hemispheric concentration is higher by about 0.8 ppbv, implying the northern hemispheric N2O emission is stronger mainly because of land emissions. Some characteristic patterns caused by surface N2O emissions and by the atmospheric transport in this observation area were seen in the latitudinal distribution. One is a maximum value at 30?N due to local N2O emissions, and the other steep concentration gradient from the equator to 20° S due to SPCZ, which seems to block smooth N2O transport form the north to south hemisphere. The N2O growth rate showed the interannual variation with period of about 3 years and its maximum around 1999-2000 at most positions. The growth rates also tended to present their phase propagations from west to east in the northern Pacific, and from low to high latitudes in the western Pacific. In order to investigate causes for the interannual variations in terms of surface N2O emissions, correlation factors between climate factors and the N2O growth rate were calculated, for the northern and southern hemisphere. As the results, soil water showed the highest correlation in each hemisphere. That is possibly thought to reflect that N2O emission from soils is the primary factor for the interannual variation of atmospheric N2O concentration in this observation area. The MEI (multivariate ENSO index) showed the almost complete opposite phase with the N2O growth rate for both hemispheres, which were almost comparable with soil water in terms of the correction factor value. It is indicated that ENSO-related changes in oceanic emission and atmospheric transport also have important roles for atmospheric N2O concentration variations in this Pacific area. These observation results were also considered, by using AGCM (Atmospheric General Circulation Model) nudged with meteorological data. Some kinds of surface flux data were used to see effects of local N2O emissions. However, main purpose of the model simulations is to examine effects of the atmospheric transport on the N2O concentration for long term, in order to compensate analyses of the emission effects above. We will present these model results, together with the observation results.