The biologically effective ultraviolet irradiance at the earth's surface varies with the elevation of the sun, the atmospheric ozone amount, and with the abundance of scatterers and absorbers of natural and anthropogenic origin. Taken alone, the reported decrease in column ozone over the Northern Hemisphere between 1969 and 1986 implies an increase in erythemal irradiance at the ground of four percent or less during summer. However, an increase in tropospheric absorption, arising from polluting gases or particulates over localized areas, could more than offset the predicted enhancement in radiation. Any such extra absorption is likely to be highly regional in nature and does not imply that a decrease in erythemal radiation has occurred on a global basis. The Antarctic ‘ozone hole’ represents a special case in which a portion of the earth has experienced ultraviolet radiation levels during spring that are far in excess of those which prevailed prior to the present decade.

[1] As part 1 in a series of papers describing long-term simulations using the Community Multiscale Air Quality (CMAQ) modeling system and subsequent process analyses and sensitivity simulations, this paper presents a comprehensive model evaluation for the full year of 2001 over the continental U.S. using both ground-based and satellite measurements. CMAQ is assessed for its ability to reproduce concentrations and long-term trends of major criteria pollutants such as surface ozone (O 3 ) and fine particulate matter (PM 2.5 ) and related variables such as indicator species, wet deposition fluxes, and column mass abundances of carbon monoxide (CO), nitrogen oxides (NO 2 ), tropospheric ozone residuals (TORs), and aerosol optical depths (AODs). The domain-wide and site-specific evaluation of surface predictions shows an overall satisfactory performance in terms of normalized mean biases for annual mean maximum 1 h and 8 h average O 3 mixing ratios (À11.6 to 0.1% and À4.6 to 3.0%, respectively), 24 h average concentrations of PM 2.5 (4.2-35.3%), sulfate (À13.0 to 43.5%), and organic carbon (OC) (À37.6 to 24.8%), and wet deposition fluxes (À13.3 to 31.6%). Larger biases, however, occur in the concentrations and wet deposition fluxes of ammonium and nitrate domain-wide and in the concentrations of PM 2.5 , sulfate, black carbon, and OC at some urban/suburban sites. The reasons for such model biases may be errors in emissions, chemistry, aerosol processes, or meteorology. The evaluation of column mass predictions shows a good model performance in capturing the seasonal variations and magnitudes of column CO and NO 2 , but relatively poor performance in reproducing observed spatial distributions and magnitudes of TORs for winter and spring and those of AODs in all seasons. Possible reasons for the poor column predictions include the underestimates of emissions, inaccurate upper layer boundary conditions, lack of model treatments of sea salt and dust, and limitations and uncertainties in satellite data.Citation: Zhang, Y., K. Vijayaraghavan, X.-Y. Wen, H. E. Snell, and M. Z. Jacobson (2009), Probing into regional ozone and particulate matter pollution in the United States: 1. A 1 year CMAQ simulation and evaluation using surface and satellite data,

This paper describes a rapid and accurate technique for the numerical modeling of band transmittances and radiances in media with nonhomogeneous thermodynamic properties (i.e., temperature and pressure), containing a mixture of absorbing gases with variable concentrations. The optimal spectral sampling (OSS) method has been designed specifically for the modeling of radiances measured by sounding radiometers in the infrared and has been extended to the microwave; it is applicable also through the visible and ultraviolet spectrum. OSS is particularly well suited for remote sensing applications and for the assimilation of satellite observations in numerical weather prediction models. The novel OSS approach is an extension of the exponential sum fitting of transmittances technique in that channel-average radiative transfer is obtained from a weighted sum of monochromatic calculations. The fact that OSS is fundamentally a monochromatic method provides the ability to accurately treat surface reflectance and spectral variations of the Planck function and surface emissivity within the channel passband, given that the proper training is applied. In addition, the method is readily coupled to multiple scattering calculations, an important factor for treating cloudy radiances. The OSS method is directly applicable to nonpositive instrument line shapes such as unapodized or weakly apodized interferometric measurements. Among the advantages of the OSS method is that its numerical accuracy, with respect to a reference line-by-line model, is selectable, allowing the model to provide whatever balance of accuracy and computational speed is optimal for a particular application. Generally only a few monochromatic points are required to model channel radiances with a brightness temperature accuracy of 0.05 K, and computation of Jacobians in a monochromatic radiative transfer scheme is straightforward. These efficiencies yield execution speeds that compare favorably to those achieved with other existing, less accurate parameterizations.

The decrease in atmospheric ozone over Antarctica during spring implies enhanced levels of ultraviolet (UV) radiation received at the earth's surface. Model calculations show that UV irradiances encountered during the occurrence of an Antarctic "ozone hole" remain less than those typical of a summer solstice at low to middle latitudes. However, the low ozone amounts observed in October 1987 imply biologically effective irradiances for McMurdo Station, Antarctica, that are comparable to or greater than those for the same location at December solstice. Life indigenous to Antarctica thereby experiences a greatly extended period of summerlike UV radiation levels.

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Satellites contribute data vital to modeling air quality, especially because of their ability to monitor global patterns from aloft. To make best use of the data and create robust models, investigators need to be aware of how the data are rendered. Scientists from Atmospheric & Environmental Research, Inc., provide a synopsis of the acquisition and processing of satellite data for potential application in air-quality modeling. The focus is on U.S.-based missions and a few Canadian- and European-based missions.

Abstract. This work assesses the impact of uncertainties in atmospheric state knowledge on retrievals of carbon dioxide column amounts (XCO 2 ) from laser differential absorption spectroscopy (LAS) measurements. LAS estimates of XCO 2 columns are normally derived not only from differential absorption observations but also from measured or prior knowledge of atmospheric state that includes temperature, moisture, and pressure along the viewing path. In the case of global space-based monitoring systems, it is often difficult if not impossible to provide collocated in situ measurements of atmospheric state for all observations, so retrievals often rely on collocated remote-sensed data or values derived from numerical weather prediction (NWP) models to describe the atmospheric state. A radiative transfer-based simulation framework, combined with representative global upper-air observations and matched NWP profiles, was used to assess the impact of model differences on estimates of column CO 2 and O 2 concentrations. These analyses focus on characterizing these errors for LAS measurements of CO 2 in the 1.57-μm region and of O 2 in the 1.27-μm region. The results provide a set of signal-to-noise metrics that characterize the errors in retrieved values associated with uncertainties in atmospheric state and provide a method for selecting optimal differential absorption line pairs to minimize the impact of these noise terms.

FASE is a line-by-line (LBL) atmospheric radiation code, grounded in the original USAF FASCODE (Fast Atmospheric Signature Code) line shape decomposition algorithm. The Department of Energy Atmospheric Radiation Measurement (ARM) Program and the AF/PL Geophysics Directorate jointly supported FASE which now envelops both agencies' important upgrades. ARM's LBLRTM (LBL Radiative Transfer Model authored by S.A. Clough and P.D. Brown of AER, Inc.) expanded the FASCODE algorithms to specifically address scientific and coding issues of particular concern to the climate community including: H20 and C02 continua, lineshape, radiance algorithms, sampling, vectorization, array parameterization, spectral ranges and inputloutput modes. These features have then been recombined with FASCODE non-LTE and laser options, plus shared common elements from MODTRAN (Moderate Resolution Transmittance Model, a 2 cm-band model) evolution. These include a new solar irradiance and UV cross sections. Examples of the feedback and validation between FASE and MODTRAN3 will be presented. INTRODUCTIONThe prime focus of the FASCODE for the Environment (FASE) program is to make available to the atmospheric spectroscopy community the results of on-going work sponsored by the ARM program, Department of Energy (DOE), and the Air Force Phillips Laboratory, Department of Defense (DoD). The goal of the program is to create an atmospheric radiance and transmittance model which is user-friendly and contains the latest atmospheric physics. In addition, advances from the wider radiative transfer community will be incorporated where appropriate within program constraints and resources.The origins ofFASE lie in FASCOD1B, a line-by-line code where the Voigt function has been decomposed into four primary functions to account for the Lorentz and Doppler components1 as well as associated wing continua. This rapid line-by-line code was developed by Clough and Kneizys2 and evolved into FASCOD3P (preliminary)3. DOE initiated separate funding of the FASCOD3P algorithm in 1990, leading to the Line-by-Line Radiative Transfer Model (LBLRTM)4 with major new contributions. The basic approach to developing FASE is severalfold: (1) to modify the overall program structure of FASCODE ILBLRTM so as to improve the flexibility and maintainability of the code without significant re-coding; (2) to incorporate a number of coding improvements (also to benefit the flexibility and maintainability); (3) to improve the user interface and access to individual portions of the code; and (4) to add new modules which incorporate updated physics and 194 / SPIE Vol. 2578 O-8194-1942-7/95/$6.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/16/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx