Broomfield, CO, United States
Broomfield, CO, United States

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Kim S.-W.,University of Colorado at Boulder | Kim S.-W.,National Oceanic and Atmospheric Administration | McKeen S.A.,University of Colorado at Boulder | McKeen S.A.,National Oceanic and Atmospheric Administration | And 36 more authors.
Atmospheric Chemistry and Physics | Year: 2011

Satellite and aircraft observations made during the 2006 Texas Air Quality Study (TexAQS) detected strong urban, industrial and power plant plumes in Texas. We simulated these plumes using the Weather Research and Forecasting-Chemistry (WRF-Chem) model with input from the US EPA's 2005 National Emission Inventory (NEI-2005), in order to evaluate emissions of nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs) in the cities of Houston and Dallas-Fort Worth. We compared the model results with satellite retrievals of tropospheric nitrogen dioxide (NO2) columns and airborne in-situ observations of several trace gases including NOx and a number of VOCs. The model and satellite NO2 columns agree well for regions with large power plants and for urban areas that are dominated by mobile sources, such as Dallas. However, in Houston, where significant mobile, industrial, and in-port marine vessel sources contribute to NOx emissions, the model NO2 columns are approximately 50%-70% higher than the satellite columns. Similar conclusions are drawn from comparisons of the model results with the TexAQS 2006 aircraft observations in Dallas and Houston. For Dallas plumes, the model-simulated NO2 showed good agreement with the aircraft observations. In contrast, the model-simulated NO2 is ∼60% higher than the aircraft observations in the Houston plumes. Further analysis indicates that the NEI-2005 NOx emissions over the Houston Ship Channel area are overestimated while the urban Houston NOx emissions are reasonably represented. The comparisons of model and aircraft observations confirm that highly reactive VOC emissions originating from industrial sources in Houston are underestimated in NEI-2005. The update of VOC emissions based on Solar Occultation Flux measurements during the field campaign leads to improved model simulations of ethylene, propylene, and formaldehyde. Reducing NOx emissions in the Houston Ship Channel and increasing highly reactive VOC emissions from the point sources in Houston improve the model's capability of simulating ozone (O3) plumes observed by the NOAA WP-3D aircraft, although the deficiencies in the model O3 simulations indicate that many challenges remain for a full understanding of the O3 formation mechanisms in Houston. © 2011 Author(s).

Liang Q.,NASA | Liang Q.,Universities Space Research Association | Atlas E.,University of Miami | Blake D.,University of California at Irvine | And 4 more authors.
Atmospheric Chemistry and Physics | Year: 2014

We use the NASA Goddard Earth Observing System (GEOS) Chemistry Climate Model (GEOSCCM) to quantify the contribution of the two most important brominated very short lived substances (VSLSs), bromoform (CHBr3) and dibromomethane (CH2Br2), to stratospheric bromine and its sensitivity to convection strength. Model simulations suggest that the most active transport of VSLSs from the marine boundary layer through the tropopause occurs over the tropical Indian Ocean, the tropical western Pacific, and off the Pacific coast of Mexico. Together, convective lofting of CHBr3 and CH2Br2 and their degradation products supplies ∼8 ppt total bromine to the base of the tropical tropopause layer (TTL, ∼150 hPa), similar to the amount of VSLS organic bromine available in the marine boundary layer (∼7.8-8.4 ppt) in the active convective lofting regions mentioned above. Of the total ∼8 ppt VSLS bromine that enters the base of the TTL at ∼150 hPa, half is in the form of organic source gases and half in the form of inorganic product gases. Only a small portion (<10%) of the VSLS-originated bromine is removed via wet scavenging in the TTL before reaching the lower stratosphere. On average, globally, CHBr3 and CH2Br2 together contribute ∼7.7 pptv to the present-day inorganic bromine in the stratosphere. However, varying model deep-convection strength between maximum (strongest) and minimum (weakest) convection conditions can introduce a ∼2.6 pptv uncertainty in the contribution of VSLSs to inorganic bromine in the stratosphere (Bry VSLS). Contrary to conventional wisdom, the minimum convection condition leads to a larger Bry VSLS as the reduced scavenging in soluble product gases, and thus a significant increase in product gas injection (2-3 ppt), greatly exceeds the relatively minor decrease in source gas injection (a few 10ths ppt). © Author(s) 2014.

Saiz-Lopez A.,Laboratory for Atmospheric and Climate Science | Lamarque J.-F.,U.S. National Center for Atmospheric Research | Kinnison D.E.,U.S. National Center for Atmospheric Research | Tilmes S.,U.S. National Center for Atmospheric Research | And 12 more authors.
Atmospheric Chemistry and Physics | Year: 2012

We have integrated observations of tropospheric ozone, very short-lived (VSL) halocarbons and reactive iodine and bromine species from a wide variety of tropical data sources with the global CAM-Chem chemistry-climate model and offline radiative transfer calculations to compute the contribution of halogen chemistry to ozone loss and associated radiative impact in the tropical marine troposphere. The inclusion of tropospheric halogen chemistry in CAM-Chem leads to an annually averaged depletion of around 10% (∼2.5 Dobson units) of the tropical tropospheric ozone column, with largest effects in the middle to upper troposphere. This depletion contributes approximately-0.10 W m -2 to the radiative flux at the tropical tropopause. This negative flux is of similar magnitude to the ∼0.33 W m∼2 contribution of tropospheric ozone to present-day radiative balance as recently estimated from satellite observations. We find that the implementation of oceanic halogen sources and chemistry in climate models is an important component of the natural background ozone budget and we suggest that it needs to be considered when estimating both preindustrial ozone baseline levels and long term changes in tropospheric ozone. © 2012 Author(s).

Wolff C.A.,Earth Observing Laboratory | Wolff C.A.,U.S. National Center for Atmospheric Research | Adriaansen D.R.,Earth Observing Laboratory | Adriaansen D.R.,U.S. National Center for Atmospheric Research | And 2 more authors.
Transactions of Japanese Society for Medical and Biological Engineering | Year: 2013

In-flight icing is a significant hazard in Alaska as the atmospheric environment is complex and ranges from maritime to continental and temperate to polar. An analysis of radiosonde data conditions for different climate zones reveals a high frequency of icing conditions year-round, varying with season and altitude. Many locations in Alaska depend on air travel for transportation, especially in smaller aircraft that fly at icing-prone altitudes. Thus, accurate diagnoses and forecasts of the icing environment, tuned to these varying conditions, are needed. Icing products are currently under development that are anticipated to meet the needs of aviation users in Alaska. The forecast product will be available first and is based on the Forecast Icing Product, originally developed for use in the CONUS, and predicts icing probability, supercooled large drop potential, and severity. The current spatial resolution is 13 km; high-resolution (3-km) model runs have also been used in the Alaska forecast algorithm to assess their value. An icing diagnosis algorithm that combines observations with model output, much like the Current Icing Product, is also in early development. To improve that product, the use of polar orbiting satellite data is being explored. These observations may be added to the diagnosis algorithm to provide observations where geostationary satellite data are not available.

Moharreri A.,Clarkson University | Craig L.,Clarkson University | Rogers D.C.,Earth Observing Laboratory | Dhaniyala S.,Clarkson University
Aerosol Science and Technology | Year: 2013

The design of a new aerosol sampler, called the blunt-body aerosol sampler (BASE), to sample interstitial particles inside clouds while avoiding the problem of cloud droplet shatter artifacts is introduced. The primary design feature of the inlet is a blunt body that houses an aerosol inlet toward its aft end. The housing is designed to be blunt enough to deflect large cloud particles traveling around the body while being streamlined enough to maintain an attached boundary layer under aircraft flow conditions. The attached flow requirement ensures that shatter particles formed from the impaction of cloud droplets on the blunt body are retained close to the surface of the body. A region of large particle shadow is, thus, created in the aft of the blunt-body housing, where an aerosol inlet can sample interstitial particles in the absence of cloud particles. Computational fluid dynamics (CFD) simulations are used to optimize the shape of the blunt body, and the final sampler design is predicted to sample particles smaller than 2 μm from the freestream while being uninfluenced by cloud droplet shatter particles of the same size. Wind tunnel tests were performed on a prototype model to confirm the attached nature of the boundary layer flow around the blunt body and to establish the size-dependent behavior of shatter particles in the vicinity of the housing. While the experiments provide initial validation of the interstitial inlet design concept, some discrepancies were observed between the wind tunnel tests and CFD predictions, suggesting a need for improvements in simulations, inlet design, and/or test methodology. Initial analyses of field data obtained from the first aircraft deployment of BASE confirm that sampling of shatter-free interstitial aerosol is possible with the inlet, but full performance characterization of BASE will require significant additional aircraft-based experiments under a range of cloud conditions. Copyright © 2013 American Association for Aerosol Research.

Craig L.,Clarkson University | Moharreri A.,Clarkson University | Schanot A.,Earth Observing Laboratory | Rogers D.C.,Earth Observing Laboratory | And 2 more authors.
Aerosol Science and Technology | Year: 2013

Aircraft-based aerosol sampling in clouds is complicated by the generation of shatter artifact particles from aerodynamic or impaction breakup of cloud droplets and ice particles in and around the aerosol inlet. Aerodynamic breakup occurs when the Weber number of a droplet, which primarily depends on the droplet size and the magnitude of the relative motion of the droplet and the local air mass, exceeds a critical value. Impaction breakup of a droplet occurs when the droplet's impaction breakup parameter, K, which is a combination of Weber and Ohnesorge numbers, exceeds a critical value. Considering these two mechanisms, the critical breakup diameters are estimated for two aerosol inlets of different designs - a conventional forward-facing solid diffuser inlet (SDI) and a cross-flow sampling sub-micron aerosol inlet (SMAI). From numerical simulations, it is determined that cloud droplets of all sizes will experience impaction breakup in SDI, while only droplets larger than ∼16 μm will experience impaction breakup in SMAI. The relatively better in-cloud sampling performance of SMAI is because of its cone design that slows the flow just upstream of the sample tube. The slowing upstream flow, however, causes aerodynamic breakup of drops larger than ∼100 μm. The critical breakup diameters determined from analysis of field data largely validate numerical predictions. The cross-flow sampling design of SMAI is seen to ensure that shatter artifacts in the inlet are minimal even when there are a significant number of particles larger that the critical breakup size. The study results, thus, suggest that the SMAI design presents an effective approach to sample interstitial particles from aircraft. © 2013 American Association for Aerosol Research.

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