Urban Air Quality
As population increases, and demographics shift, cities are growing larger. This poses questions as to the quality of the air
within and downwind of large urban areas. LAR is involved with urban air quality research in order to help characterize the
chemical/physical transformations of gases and aerosols within the urban area, to determine the ultimate fate of pollutants
exported from urban areas, and to assess the current and future impacts of these exported pollutants on regional and global
air quality, ecosystems, and climate. LAR is involved in both coordinated observations from ground based stations and satellites,
and regional and global models of the transport and transformations of urban pollutants.
LAR with collaborators at the National Center for Atmospheric Research (NCAR) have recently developed the highly flexible
disjunct eddy covariance (DEC) technique. Within LAR, this technique has already been used with a proton transfer reaction
mass spectrometer (PTR-MS) to measure fluxes of trace organic species in urban environments. We are now expanding this
capability to also allow us to measure fluxes of NH3, NOx species, and aerosol properties. These flux measurements are
complemented by an extensive range of ground-based observational tools, including real-time mass spectrometry of organic
gases, characterization of halogen gases, HOx, NOx, O3, NH3, and SF6 via differential optical absorption spectroscopy (DOAS)
and other spectrometric techniques, real-measurement of aerosol number and size distribution, and filter sampling techniques
for aerosol composition.
Another modeling capability within LAR (in conjunction with Mechanical and Material Engineering) is computational fluid dynamic
(CFD) modeling. Applications of this work have addressed transport and dispersion within an urban environment where the
commercial FLUENT code was used to simulate tracer releases within central Oklahoma City. These tracer tests were conducted
as part of the Joint Urban 2003 field campaign. LAR was involved in tracer measurements during the campaign, and then used
the FLUENT model to simulate specific tracer tests from the campaign. A k-e simulation was employed with a grid size as small
as 3 m in the vicinity of the source.
In this work, we collected volatile organic carbon (VOC) flux measurements at a site near the center of Mexico City as
part of the large MILAGRO field campaign. We employed a fast olefin sensor to measure olefin fluxes, a PTR-MS to measure
fluxes of aromatics and selected oxygenated VOC, and a disjunct eddy accumulation system to measure fluxes of other
individual VOC amenable to analysis with gas chromato- graphy/flame ionization detection. Fluxes of CO, CO2 and latent
and sensible heat flux were also measured. The flux measure- ments were conducted on a continuous basis for appromimately
one month in Mexico City and provided a detailed data base of urban fluxes that are being used to support the analysis of
MIRAGE urban plume transport and chemistry.
Graduate student Rasa Grivicke in Mexico City
At a second site northwest of Mexico City, in collaboration with researchers outside of LAR, we characterized the
composition of freshly formed particles and compared their composition and formation rate with the concentrations of
suspected precursor gases, including ammonia. These data will improve our understanding of the importance of new
particle formation in heavily polluted atmospheres.
LAR is conducting research on hydrocarbon profiles over western Houston. Struggling with a smog problem, the city of Houston
is seeking to better understand the impact of emissions from large petrochemical operations in the region on air quality.
Working with several government agencies, LAR researchers will use a proton transfer reaction mass spectrometer to carefully
measure emissions of organic compounds in various areas of the city that are impacted by either petrochemical operations,
auto emissions, or biogenic sources, such as trees.
Petrochemical refinery, Houston
The aim of this work is to understand the role of reactive halogen gases (Cl2, Br2,
BrCl, and I2) on ozone formation and
loss rates in polluted coastal areas. These halogen gases are thought to be present due to chemical processing of sea-salt
particles. Reactions of these gases with urban air pollution can lead to increased rates of ozone and particle formation.
Understanding their role is necessary for urban airshed air quality monitoring and planning mitigation strategies to reduce
urban ozone and particle concentrations in California and elsewhere. Measurements of these gases, selected halogen oxides,
and selected organohalogen photoproducts have been made at a coastal site near Los Angeles to quantify their impact on ozone
Ozone study in Malibu, CA
MF-DOAS ground-based satellite validations for NO2 and O3
A MultiFunction Differential Optical Absorption Spectroscopy (MF-DOAS) instrument has been developed for ground based
validation of the Aura Satellite/Ozone Monitoring Instrument (OMI) and for measurement of urban air pollution. The MF-DOAS
instrument was fielded in prototype form at Pacific Northwest National Laboratory in Richland, WA from mid-April to mid-May
2006. The MF-DOAS instrument is unique in its ability to take both scattered sky measurements and direct sun measurements.
This combination allows measurement of air pollution with simple stratospheric air mass factors from the direct sun and also
makes use of the MAX-DOAS azimuth/elevation technique coupled with a spherical radiative transfer code to derive spatial and
full day temporal dependence of urban pollutants. The tropospheric NO2 pollution trends are captured by the MF-DOAS instrument
as confirmed by in-situ measurements. Overall, the tropospheric spatial variation of NO2 from MF-DOAS and OMI correlate well.