Atmospheric & Oceanic Science
Permanent URI for this communityhttp://hdl.handle.net/1903/2264
Formerly known as the Department of Meteorology.
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Item An evaluation of a severe smog episode in the Eastern U.S. using regional modeling and satellite measurements(2011) Yegorova, Elena Andreyevna; Dickerson, Russell R; Allen, Dale J; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An ensemble of regional chemical modeling (WRF/Chem with RADM2) simulations, satellite, ozonesonde, and surface observations during July 7-11, 2007 was used to examine the horizontal and vertical signature of one of the worst smog events in the eastern U.S. in the past decade. The general features of this event -- a broad area of high pressure, weak winds and heavy pollution, terminated by the passage of a cold front -- were well simulated by the model. Average 8-hr maximum O3 has a mean (±Σ) bias of 0.59 (±11.0) ppbv and a root mean square error of 11.0 ppbv. WRF/Chem performed the best on poor air quality days, simulating correctly the spatial pattern of surface O3. Yet the model underpredicted O3 maxima by 5-7 ppbv in the Northeast and overpredicted by 8-11 ppbv in the Southeast. High O3 biases in the Southeast are explained by overpredicted temperatures in the model (>1.5°C). Sensitivity simulations with 1) accelerated O3 dry deposition velocity and 2) suppressed multiphase nitric acid formation pushed the model closer to observations. Simulated O3 vertical profiles over Beltsville, MD showed good agreement with ozonesonde measurements, but the modeled boundary layer depth was overpredicted on July 9, contributing to the low bias over this region. During this severe smog episode, space-borne TES detected high total tropospheric column ozone (TCO) over the Western Atlantic Ocean off the coast near North and South Carolina. The standard product (OMI/MLS) missed the magnitude of these local maxima, but the level-2 ozone profile (OMI) confirmed the TES observations. HYSPLIT back trajectories from these O3 maxima intersected regions of strong convection over the Southeast and Great Lakes regions. When lightning NO emissions were implemented in WRF/Chem, the high concentrations of NOx and O3 off the coast were well reproduced, showing that the exported O3 was produced by a combination of natural NO and pollutants lofted from the lower atmosphere. Lastly, WINTER MONEX O3 data from 1978 are presented for the first time here in discussion of open cell convection over Indonesia.Item Validation of SO2 retrievals from the Ozone Monitoring Instrument (OMI) over NE China(American Geophysical Union (AGU), 2008) Krotkov, N. A.; McClure, B.; Dickerson, R. R.; Carn, S.; Li, C.; Bhartia, P. K.; Yang, K.; Krueger, A.; Li, Z.; Levelt, P. F.; Chen, Hongbin; Wang, Pucai; Lu, DarenThe Ozone Monitoring Instrument (OMI) launched on the NASA Aura satellite in July 2004 offers unprecedented spatial resolution, coupled with contiguous daily global coverage, for space-based UV measurements of sulfur dioxide (SO2). We present a first validation of the OMI SO2 data with in-situ aircraft measurements in NE China in April 2005. The study demonstrates that OMI can distinguish between background SO2 conditions and heavy pollution on a daily basis. The noise (expressed as the standard deviation, σ) in the PBL SO2 data is ~1.5DU (Dobson Unit, 2.691016 molecules/cm2) for instantaneous field of view (IFOV) data. By looking at the pristine South Pacific under optimal conditions we have determined that temporal and spatial averaging can improve the resolution of the instrument to σ ~ 0.3 DU; the long term average over this remote location was within 0.1 DU of zero. Under polluted conditions, however, Collection 2 data are higher than aircraft measurements by a factor of two in most cases. Parameterization of the airmass factor (AMF) appears to enhance the accuracy of the SO2 data. Improved calibrations of the radiance and irradiance data (Collection 3) result in better agreement with aircraft measurements on polluted days. The re-processed and AMF-corrected Collection 3 data still show positive bias and sensitivity to UV absorbing aerosols. The difference between the in situ data and the OMI daily PBL SO2 measurements within 30 km of the aircraft profiles was about 1 DU, equivalent to ~5 ppb from 0 to 3000 m altitude. Quantifying the SO2 profile and spectral dependence of aerosol absorption between 310 and 330 nm are critical for accurate estimates of SO2 from satellite UV measurements.