Atmospheric Sciences IV Posters
Presiding: W A Abdou, Jet Propulsion Laboratory, California Institute of Technology; K Chance, Harvard-Smithsonian Center for Astrophysics
A21A-01 0830h
Comparing Aerosol Properties Measured by the SAGE II and SAGE III Satellite Experiments
SAGE II and SAGE III are two currently operating satellite systems designed to measure aerosol extinction coefficients and concentrations of trace gases in the atmosphere by using the techniques of solar and/or lunar occultation. Since February 2002, there are occasions when measurement locations for both satellites are nearly coincident, thereby providing opportunities for a measurement comparison. In this paper, the coincidences in the years from 2002 to 2004 are identified. Aerosol properties, including extinctions, optical depths, surface area densities, and volume densities measured by SAGE II and SAGE III at these coincidences are compared. The retrieval errors for the SAGE II and SAGE III are discussed. It was found that generally in the main aerosol layer, between about 18 to 26 km, the differences are less than about 30%. Larger differences are shown at altitudes near the tropopause and around 30 km. The contribution of measurement uncertainties to the differences in aerosol properties is also discussed.
A21A-02 0830h
Where Did All the Ozone Go? : An Analysis of Tropospheric Ozonesondes from the IONS Campaign During the Summer of 2004 in the Northeastern US and Canada
A short-term ozonesonde network was formed in July-August 2004 to coordinate ozonesonde launches during the multi-site, multi-aircraft campaign called ICARTT/INTEX/NEAQS (International Consortium on Atmospheric Research on Transport and Transformation)/Intercontinental Transport Experiment/New England Air Quality Study. In IONS (INTEX Ozonesonde Network Study (http://croc.gsfc.nasa.gov/intex/ions.html ), nearly 300 soundings were launched from eleven North American stations and an oceanographic ship in the Gulf of Maine. The INTEX study region was dominated by a series of weak frontal systems that mixed aged pollution with stratospheric ozone in the middle troposphere. We have used meteorological tracers such as potential vorticity to examine cases of stratospheric intrusion over the INTEX campaign period at several of the sites. In addition, we are using a non hierarchical clustering method to look for distinct climate differences in sondes collected in 2004 at Wallops Island and comparing these with sondes taken at this station over the previous 10 years. The analysis suggests that indeed the meteorological conditions of the summer of 2004 led to reduced levels of ozone in the troposphere.
A21A-03 0830h
MISR BRF measurements for various surface types: Intercomparison with coincident airborne and ground measurements.
The BRF retrieved by the multiangle Imaging spectroRadimeter (MISR) are compared with those coincidently measured from aircraft, by the Cloud Absorption Radiometer (CAR) and MISR airborne simulator (AirMISR), and on the ground, by the Portable Apparatus for Rabid Acquisition of Bidirectional Observations of Land and Atmosphere (PARABOLA III). The intercomparisons are made for five types of surfaces: bright desert, salt pans, dark grassland, forests and dismal swamps. The results show that MISR BRF values are within +/- 10% in agreement with the corresponding airborne and ground measurements, independent of the surface type. This study is part of an effort to validate MISR surface products.
A21A-04 0830h
Spatio-Temporal Distributions of Particulate Matter and Heavy Metal Exposures in Washington, DC
The District of Columbia ranks seventh highest as one of the unhealthiest places to live due to poor air quality (EPA Report, 1999). Particulate matter is one of the major contributors to pollution in the Washington, DC environment. Quite often ambient airborne toxics are closely associated with particulate matter. Fine aerosols are characterized as particles with diameters smaller than 1m and are easily deposited into the alveolar regions of the human lungs, which can impose severe health risks. In this study, high-resolution aerosol measurements of PM2.5 and heavy metals like chromium, lead, cadmium and arsenic, in four wards of Washington, DC have been performed. Spatial distributions of both aerosols and heavy metals are characterized as a function of size and mass properties. This paper presents results of the spatial analysis of aerosol number and mass distribution for PM2.5.
A21A-05 0830h
FUTBOLIN (Full Transfer by Ordinary LINe-by-line methods): a new Radiative Transfer Code for Atmospheric Calculations in the Visible and Infrared
FUTBOLIN is a new algorithm to calculate line-by-line atmospheric emission/transmission spectra for planetary atmospheres in the 0.3 - 1000 microns spectral region (visible, near-Infrared, infrared, and far-infrared). The code has been compared with others, like GENLN2 and MODTRAN, and has been applied to the analysis of Earth and Titan' spectra. It reads the spectral lines in HITRAN or GEISA format. The interaction with the code is extremely user-friendly. In addition to the spectroscopic file, and for the simplest calculation, the only mandatory input file is that containing the atmospheric profiles of the species involved in the calculation; but the user can control the calculation up to the finest detail (radius of the planet, spectral range, spectral sampling, irregular grid files, tangent altitudes to be covered in the calculation, filed-of-view or instrument line shape convolutions, spherical or plane-parallel atmosphere treatment, CO2 line mixing, continuum absorption from H2O, O2, N2 and CO2, treatment for rotational, electronic or rotational non-Local Thermodynamic Equilibrium (non-LTE) effects, selection of particular isotopes and bands, jacobians, viewing geometries, surface reflections, monochromatic and spectral albedo, types and combinations of clouds and coverage,...). The main purpose of FUTBOLIN is to generate spectra. Output options are radiance, transmission, absorption or optical depth spectra, infrared cooling rate spectra, radiance flux spectra, absorption coefficient, and cloud radiative effect ("cloud forcing") among others.
A21A-06 0830h
High Resolution Aerosol Retrievals from ETM+ Over Urban Areas
Satellite monitoring of the main sources of the man-made pollutants is important to understand the climate forcing of anthropogenic aerosols. Over land, the aerosol retrievals are most accurate over dark dense vegetation (DDV). In the urban/industrial areas the DDV targets are small, often varying from a few tens of meters (clumps of trees) to several hundred meters (small fields and parks), and can only be captured by the high-resolution sensors. In this case, because of the high surface heterogeneity and focus on the dark pixels, the traditional aerosol retrievals based on 1D radiative transfer (RT) theory have a substantial bias. We developed a new dark target method for unbiased simultaneous retrieval of the aerosol model and optical thickness over land from Landsat ETM+ data, based on 3-D RT theory. The method automatically selects an aerosol model from a large set of candidate models using statistical approach of probability distribution function. The aerosols are retrieved in the blue and red bands relying on prediction of the surface reflectance in these bands from the shortwave infrared region (2.1-2.2 mkm). We will describe the developed method and its validation with AERONET measurements for a set of ETM+ images of the Washington-Baltimore area.
A21A-07 0830h
Assimilation of MOPITT CO Retrievals into the GMAO Constituent Assimilation System
We present initial results of assimilating weighted column averages of CO data from MOPITT into the GMAO constituent assimilation system. MOPITT is a nadir sounding instrument that makes use of spectrally distinct channels which peak at different altitudes in order to retrieve CO profiles. Associated with the profile retrievals are averaging kernels, which indicate the contribution of each atmospheric layer to the total column CO. This vertical dependence is included in the assimilation by applying the averaging kernels to the background CO field, in order to weight them in a manner consistent with the MOPITT observations. The background fields are provided by an on-line transport calculation in the GEOS-4 General Circulation Model, coupled to a parameterized chemistry module, using production rates and loss frequencies derived from the GEOS-Chem model at Harvard University. Estimates of surface sources of CO are determined daily from space-based observations of biomass burning, along with climatological distributions of fossil-fuel emissions. The focus of the analysis is on the northern summer of 2004, over the period of the Intex-NA field mission, with an examination of the impacts of assimilation on estimates of CO in- and out-flow through the boundaries of North America.
A21A-08 0830h
Space-Based Constraints on North American Emissions of Nitrogen Oxides
Global emission inventories of nitrogen oxides (NOx) remain uncertain to a factor of 2 with substantial implications for understanding of surface air quality, atmospheric oxidation, and climate. We will discuss recent progress in improving NOx emission inventories by combining traditional bottom-up inventories with top-down constraints from the GOME and SCIAMACHY satellite instruments. This integration results in an optimized surface NOx emission inventory with lower uncertainties. Additionally, comparisons with in-situ NO2 profile measurements during the ICARTT campaign (summer 2004) will be shown to establish the validity and quantify the accuracy of the SCIAMACHY tropospheric NO2 column abundances.
A21A-09 0830h
The Transport and Regional Aerosol Impact of Volcanic Ash from the July, 2003 Soufriere Hills Volcanic Eruption
The Soufriere Hills Volcano is located on the southern half of the Caribbean island of Montserrat. Montserrat is situated in the northern part of the Lesser Antilles, which is a volcanic island arc formed along the junction of the Atlantic tectonic plate and the Caribbean plate. An eruption of the Soufriere Hills Volcano began in 1995. Periods of small to moderate sized explosions followed. On July 12, 2003, a lava-dome of the volcano collapsed and led to several days of explosions that rocked the island and injected ash into the atmosphere. The aim of this work is to analyze the transport mechanism of the volcanic ash from the island of Montserrat to the southwestern coast of Puerto Rico and clarify its impact on regional aerosol distributions.
A21A-10 0830h
Atmospheric Nitrogen Deposition and its Potential Effects on the Mullica River-Great Bay Ecosystem in Southern New Jersey
To characterize atmospheric inorganic nitrogen deposition to the Mullica River-Great Bay Estuary and to examine its impact on the coastal ecosystem, atmospheric sampling has been conducted at Tuckerton in southern New Jersey since March 2004. A total of 43 precipitation samples have been collected on an event basis using a wet-only automatic precipitation sampler. A total of 23 aerosol samples were also taken during this period of time with a high-volume aerosol sampler. Chemical analysis was performed using a Dionex Ion Chromatograph to determine the concentrations of nitrate and ammonium in precipitation and associated with aerosols. Atmospheric deposition of nitrate and ammonium were calculated using simple wet and dry atmospheric deposition models. The results show that nitrate and ammonium concentrations vary strongly with season, and the highest concentrations were observed during the spring. The average concentrations in precipitation for nitrate and ammonium in the samples collected to date are 2.41 mg l-1 and 0.56 mg l-1, respectively. The average aerosol concentrations are 3.7 Μg m-3 for nitrate and 1.5 Μg m-3 for ammonium. The results also indicate that wet deposition is the main contributor to the atmospheric nitrogen entering the Mullica River-Great Bay Estuary. High wet deposition rates of nitrogen were seen in the spring and summer with total average values of 429.08 mg m-2 month-1 for the spring and 229.28 mg m-2 month-1 for the summer. These results will be combined with satellite ocean color to investigate the effect of atmospheric nitrogen deposition on coastal primary productivity in this ecosystem. The atmospheric nitrogen data can also be combined with water column nutrient data that is being collected at the Jacques Cousteau National Estuarine Research Reserve, to assist in generating a nutrient budget to better manage the coastal resources of the Mullica River-Great Bay Estuary.
A21A-11 0830h
Distribution and Sources of Lead in Urban Soil in El Paso, Texas
The geographic distribution of lead in El Paso soils is presented in maps based on 500 composite soil samples collected in the region. Each composite sample comprises equal volumes of samples taken from the public space in front of individual houses or structures around a single municipal block. The use of such composites highlights the distribution of lead at the neighborhood level, and de-emphasizes any anomalous elevated level associated with an individual house or structure. Lead levels are highest in the downtown commercial district, in the adjacent area to the east, which comprises an old central business, transport, and light industry complex, and to the west in the area of a century-old smelter, placed on standby six years ago. The continuity of this zone, and the age of its structures, make it difficult to differentiate lead sources. Lead values decrease systematically away from this urban core zone, with the lowest levels generally encountered in the peripheral, lightly populated developments and communities. This geographic distribution of Pb in soil is consistent with Pb measurements reported on particulate matter taken from four air monitoring stations during the 1990s. Soil data thus can complement air studies by providing an essentially infinite geographic network of sampling sites that, with varying accuracy, record and integrate air conditions over years and decades. Research supported by NIEHS Grant 1RO1-ES11367.
A21A-12 0830h
Can We Detect the Solar Cycle Using the Ground-based Measurements?
Detection of trends and long-term patterns such as the solar cycle using the ground-based measurements is problematic due to the high degree of variability on daily, seasonal and annual time scales. We have approached this problem using thermal diffusion of the temperature time series in a conductive heat flow model. Thermal diffusion filters the input signals so that the amplitude diminishes exponentially with depth as a function of the period of variation and the thermal diffusivity of the medium. The result is that the detection limit of a signal varies according the relationship between signal period and depth. We have applied this filter to daily mean values for air, soil and downward radiation during the 1981-2003 period from a network of automated meteorological stations within North Dakota, South Dakota, Nebraska, and Kansas that are maintained by the High Plains Regional Climate Center. Here we present results for each of these signals as they would be filtered at a depth of 10 m. Trends of the air and soil temperatures, and downward solar radiation at the surface during the study period correlate well with each other. More important, these trends are nearly the same as the variation of phase-shifted solar irradiance at the top of atmosphere measured by satellites. One exception is the ground-based radiation data from the Kansas sites which are know to have had problems with radiation sensors. Preliminary results from this study have shown that the variations of the surface air and soil temperatures within a solar cycle range from 0.25 to 0.4oC at the Northern Great Plains. The solar irradiance at TOA during the past two solar cycles varied about 0.1% (~1.4 Wm-2), producing a climate forcing of 0.24 Wm-2 and resulting in a surface temperature change of ~0.18oC (Natural variability). Thus, the anthropogenic variation during a solar cycle will approximately be within a range of 0.07 to 0.22oC, and a more detailed study is warranted. In summary, we draw two conclusions from our observations. First, the preliminary results support the fundamental assumption of borehole paleoclimatology that air and ground temperatures are coupled on long time scales. Second, this method holds promise for investigation of links between global temperatures and solar irradiance.
A21A-13 0830h
Global Distribution of Tropospheric Ozone from GOME and Comparison with GEOS-CHEM Model Results
We present the first directly retrieved global distribution of tropospheric column ozone from satellite-based measurements. Tropospheric ozone is derived from backscattered radiance spectra in the ultraviolet measured by GOME. We validate the retrievals globally with ozonesonde observations at 33 ozonesonde stations. The retrieved tropospheric ozone well captures the temporal variability of ozonesonde observations and the biases are generally within 5 DU. The global distribution of tropospheric ozone reveals previously unrecognized features, such as bands of high ozone (e.g., 40-50 DU) at mid-latitudes during the spring and summer, and clearly shows signals due to biomass burning, air pollution, stratosphere-troposphere exchange, transport, and convection. We compare the retrievals with the global tropospheric chemistry model GEOS-CHEM; the overall structures are similar, but significant differences exist. We investigate the new ozone features with GEOS-CHEM model and other models and measurements.
A21A-14 0830h
Determining Small Scale Albedos Using High Resolution Multiangle Satellite Measurements
Current satellite short-wave (SW) albedo measurements, such as CERES's, have only a broad spatial resolution and cannot by themselves accurately measure reflectance (roughly solar "forcing") on small space and time scales. The major difficulty is that earth's surface reflectivity, including the atmosphere and clouds, is substantially anisotropic. However, accurate regional and time-dependent albedos are needed for studying causes of climate variability and change, and improving models from global to at least cloud resolving scales. A first step to obtain these albedos, for which we show results, is to accurately relate (and verify) the high resolution spatial and angular surface narrow-band MISR (Multi-Angle Imaging Spectroradiometer) radiance measurements aboard the Terra satellite to coincident total shortwave broadband (SWB) low resolution measurements from the onboard CERES instrument. Because MISR measures radiance of the same points along an orbital swath, it becomes possible to check and improve Angular (reflection) Distribution Models (ADMs) at small scales (< 1 km). The ADMs can later be used to invert a measured angular radiance to a local albedo. The difficulty lies in obtaining accurate ADMs for earth's highly varied surface and lighting conditions. We show prediction accuracy examples of CERES SWB vs. single and multiple band MISR data regressions. We include view angle dependence (9 angles: nadir plus 26, 46, 60, and 70 degrees fore and aft) and show improved accuracy when surface data, e.g., solar zenith and scattering angle, and surface type are included. In many cases, we predict angular (bidirectional) reflectance to ~ 0.01, or about 10 watts/sq m in irradiance. We also show examples of "difficult" scene types, such as varying levels of broken clouds, where accuracy degrades by a factor of ~2.
A21A-15 0830h
Irradiance Measurement Biasing by Infrared Cooling Errors for the Eppley PSP
Global solar irradiance measurements made using Eppley Precision Pyranometers (PSP) can be biased by IR cooling errors. During the New England high resolution temperature and forecasting experiment (NEHRTP-2004) the NOAA Environmental Technology Laboratory made side-by-side comparisons of the global solar irradiance measured using PSPs and by combining separate direct and diffuse measurements utilizing pyroheliometers and 8-48 Black and White pyranometers at Concord, NH and Plymouth, MA. These measurements allowed us to quantify and correct the magnitude of the thermal offset error in the PSPs, and allowed us to use the global PSP's during periods when the solar trackers used in the experiment failed.
A21A-16 0830h
Suitability of the BP MSX 01 Photovoltaic Module for Solar Irradiance Measurements
During the summer of 2004 solar irradiance measurements were made using three BP MSX 01 photovoltaic modules, a Li-Cor LI-200SZ Pyranometer, and an Eppley Precision Spectral Pyranomter (PSP). Instrument responses to clouds were analyzed for each of the photovoltaic modules in order to determine suitability for different climates and weather patterns. Calibration shifts at low sun angles were analyzed along with nighttime responses. Response times were also analyzed to determine the suitability of the photovoltaic modules for use as a pyranometer. The three BP photovoltaic cells, Li-cor pyranometer, and Eppley PSP were all connected to a Campbell Scientific CR10X data logger. Output voltages were read as differential channels from each instrument. Observations were recorded every second, and every ten observations were averaged and stored as one data entry. The results of careful analysis showed that the BP MSX 01 photovoltaic modules should be able to be used as pyranometers in solar energy monitoring applications. By averaging the three voltaic modules as an array, the derived values were much more accurate than any one module on its own.
A21A-17 INVITED 0830h
The retrieval of aerosol optical thickness over high reflective land surface with MODIS
The algorithm of aerosol optical thickness retrieval from MODIS over low reflective land surface is matured with good consistancy. But the retrieval of aerosol optical thickness over high reflective land surface is still very challenging. In this work, a simple algorithm is developed to retrieve aerosol optical thickness over the bright surfaces. The algorithm is applied over several different typical land surface, such as dark land surface, and bright land surface. The retrieved AOT is compared with the ground measurement from sun-track photometer. It shows that the algorithm can produce a reasonable estimate of the aerosol optical thickness.
A21A-18 0830h
Stray Light Corrections in Measurements of Limb Scattered Sunlight
Measuring limb scattered sunlight has recently become a popular way of determining the vertical distribution of ozone and other atmospheric constituents. Limb scattering measurements provide broader geographic coverage than solar occultation techniques and almost as good vertical resolution. Many of the new and near future limb scatter instruments are spectral imagers. Stray light is often a significant problem for such instruments because of the large vertical and spectral contrasts in the intensity of limb scattered sunlight. In principle, stray light can be corrected for in spectral imager data by using pre-launch measurements of the impulse response functions of the electro-optical system. The impulse response functions can be determined from laboratory measurements of the instrument's point spread functions and thoughput. We discuss two techniques for using the impulse response functions to correct for stray light: (1) correcting the radiances before inverting the data for the atmospheric constituent profiles, and (2) using the impulse response functions directly in the inversion for the atmospheric constituent profiles. We present results for the first of these methods.
A21A-19 0830h
On the Use of Polarimetric Radars for Studies of Cirrostratus Clouds: Numerical Simulations and S-Band Radar Observations
Uncertainties in parameterizing clouds have been identified as important sources of error in climate model outputs. These problems are linked to insufficient data and the complex behaviors of clouds. Progress in reducing these uncertainties is being made as more data are collected and analyzed. In particular, polarimetric radars are capable of estimating microphysical cloud properties in addition to macrophysical properties. In this paper, a physical-based electromagnetic backscattering model, whose components are based on previous experimental work, is presented for diagnosing and linking cloud particle behavior to the scattered signals received. The scatterers in the model consist of prolate and oblate spheroids and the scattering regime is assumed to be Rayleigh. Inputs to the scattering model include mean drop diameter, equivalent spherical drop size distribution form, and liquid-water content. These parameters are converted to equivalent spheroids using mass conservation and diameter dependent axial ratios. A terminal fall velocity based on fall geometry is calculated and a background wind field is imposed. Finally, additional scaling and dyadic scattering of plane waves are applied to simulate the effective scattered signal. Simulation results will be presented along with comparisons to data from the S-band polarimetric radar (KOUN) operated by the National Severe Storms Laboratory in Norman, Oklahoma.
A21A-20 0830h
Geographical variability of fine and coarse mode aerosol properties derived from MFRSR datasets
A new version of data analysis algorithm for Multi-Filter Rotating Shadowband Radiometer (MFRSR) was applied to several long-term datasets to study seasonal and geographical variability of aerosol parameters. In distinction from our older method that used a monomodal aerosol size distribution, the new algorithm allows us to partition the aerosol optical thickness into fine and coarse modes. In addition we retrieve the fine mode effective radius and Angstrom exponent. A bimodal gamma distribution is used to model the aerosol particle size distribution. Development of an automated cloud screening procedure based on optical thickness variability analysis allows us to make the data processing more objective and fully automatic. The algorithm has been applied to a multi-year dataset from the local MFRSR network at the DOE Atmospheric Radiation Measurement (ARM) Program site in Southern Great Plains (SGP). Our retrieved aerosol optical thicknesses (total, fine, and coarse) are compared with AERONET almucantar retrieval results derived from a CIMEL sunphotometer co-located with the MFRSR at the SGP Central Facility. A constrained variant of the algorithm (zero nitrogen dioxide column amount) has been used to demonstrate the range of physically viable values of the fine mode effective radius, and for comparison with AERONET retrievals of particle size. A correspondence has been found between the geographical variation in the fine mode particle size and aerosol composition (nitrates vs. sulfates) as measured by National Atmospheric Deposition Program. Comparison with sampling measurements performed at the SGP's Central Facility by NOAA Pacific Marine Environmental Laboratory (PMEL) also showed correspondence in temporal (both seasonal and day-to-day) variability between our fine mode size and nitrate/sulfate ion mass concentration ratios.
A21A-21 0830h
Comparison of MODIS and MISR aerosol optical depth over Indian subcontinent for winter season 2000 to 2004
The comparison of aerosol optical depth (AOD) from MODIS and MISR sensors show high correlation for winter months (November, December and January) over the Indo-Gangetic basin. The MODIS and MISR level-3 data show a very high AOD due to high atmospheric pollutants that is found to be very dynamic in nature. The spatial variability over the basin is very much dependent on the meteorological conditions and low topography of the basin. High AOD shifts from central part of the Ganga basin towards eastern part of the basin near Kolkata with advance of winter season depending upon the wind circulation pattern. We have also compared MODIS and MISR AOD with AERONET over Kanpur region. MODIS data shows a good correlation (0.7) with AERONET compared those with MISR. The initial study reveals that MODIS AOD data is more reliable compared to MISR AOD over Kanpur which is located in the central part of the basin. MODIS and MISR AOD show much higher AOD over the central part of the basin in the year 2004 compared to other years 2000 - 2003.
A21A-22 0830h
Possibilities and Challenges in Using Satellite Data for PM2.5 Forecasts
Satellite remote sensing has brought our observation of the earth's atmosphere into a new era, and remote sensing capability could lead to a quantum leap in our ability of air quality monitoring and prediction. In terms of aerosols, the most common quantity from satellite retrieval is the atmospheric column aerosol optical thickness (AOT), and the most common quantity indicating air quality at the surface is the concentration of PM2.5. We present here the relationship between the column AOT and the surface PM2.5 from a global aerosol model GOCART and from satellite and surface measurements. We will discuss the possibilities and challenges in using satellite data for PM2.5 forecasts, and if model-satellite assimilation can improve the forecast quality.
A21A-23 0830h
Aerosol Optical and Chemical Properties in Urban Guangzhou, China
During the intensive period of the Pearl River Delta (PRD) measurement campaign (4 Oct - 5 Nov 2004), we performed in-situ measurements of aerosol chemical and optical properties (PM2.5) in urban Guangzhou (23.08N, 113.16E, altitude 8m asl; ~150 km northwest of Hong Kong). A photoacoustic spectrometer (532 nm) and two integrating nephelometers (545 nm) were used to determine aerosol light absorption (dry, RH less than 40 percent) and scattering coefficients (dry and ambient), respectively. Twelve-hour averages of elemental (EC) and organic carbon (OC) aerosol mass concentration were determined by evolved gas analysis. Ionic constituents were determined by ion chromatography. The aerosol concentrations at this urban site were consistently very high, with average PM2.5, OC and EC mass concentrations of 103, 22.3 and 7.1 æg m-3, respectively. The high average OC/EC ratio of about 3 suggests that traffic emissions are an important emission source in the sampled airshed. The average scattering and absorption coefficients for dry aerosol were 402 and 88 Mm-1, respectively. During some episodes, extremely high values of aerosol absorption were reached (up to 450 Mm-1). Consistent with the urban pollution sources and the exceptionally dry weather conditions, the average single scattering albedo (SSA) at ambient conditions was about 0.86, indicating strongly absorbing aerosol. The observed diurnal trends are consistent with particle growth by condensation during day, enhanced traffic activity in the morning and evening hours, and the build-up of a shallow nocturnal boundary layer during the night.
A21A-24 0830h
SCIAMACHY CO and CH4 Measurements Compared to MOPITT and TM3
The near-infrared spectra measured by SCIAMACHY in nadir mode on the ENVISAT satellite enable us to retrieve total columns for CH4 and CO, from which global maps can be constructed. Since these trace species play an important role in air pollution and global climate change, such a global knowledge on their distribution is a prerequisite to fully understand their role in atmospheric chemistry and climate. Scientific retrieval algorithms have been developed at SRON that make use of the calibration and characterization of the near-infrared detectors, which have been performed in-house. Such a detailed characterization appeared to be necessary due to the growth of an ice layer on the IR detectors. Despite these difficulties, there is clear evidence that SCIAMACHY is sensitive to the distribution of lower tropospheric CO and CH4. For a few months in 2003 and 2004 CO and CH4 data from SCIAMACHY have been validated. Retrieved CH4 columns compare well with results of the TM3 atmospheric chemistry transport model. Similar model results have been compared to total column CO. The latter species has also been compared with data from the satellite instrument MOPITT, which measures CO in the thermal infrared.