The Impact of Aerosols, Clouds, and Ozone on Surface UV and Photochemistry in Houston, TX

EPA Grant Number: R833225
Title: The Impact of Aerosols, Clouds, and Ozone on Surface UV and Photochemistry in Houston, TX
Investigators: Lefer, Barry , Slusser, James
Institution: University of Houston , Colorado State University
EPA Project Officer: Chung, Serena
Project Period: March 15, 2007 through March 14, 2009 (Extended to March 14, 2010)
Project Amount: $292,310
RFA: Implications of Tropospheric Air Pollution for Surface UV Exposures (2005) RFA Text |  Recipients Lists
Research Category: Global Climate Change , Air Quality and Air Toxics , Climate Change , Air


The primary objective of this study is to measure surface UV irradiance and UV actinic flux levels from several instruments in Houston, TX over an 18-month period and to use this data to examine: 1) How changes in tropospheric pollution (both aerosols and ozone) affect surface UV levels and ozone photochemistry in Houston?, 2) How clouds affect surface UV levels and ozone photochemistry in Houston? 3) How changes in UV surface levels due tropospheric pollution (both aerosols and ozone) compare to changes due to variations in the total column ozone? Based on our limited measurements in Houston from the TexAQS-2000 experiment, we hypothesize: 1) Significant reductions in surface UV levels will occur in Houston due to tropospheric pollution, primarily from the absorption of UV radiation by aerosols, 2) Changes in UV levels due to tropospheric pollution are of similar magnitude compared to total ozone column changes. 3) The combined effect of tropospheric pollution and clouds are to significantly suppress photochemical ozone formation in Houston.


The Moody Tower on the University of Houston – Main Campus has is a new atmospheric radiation and chemistry measurement facility. In addition to continuous measurements of basic chemical species (O3, CO, NO, NO2, PAN, VOCs, and standard meteorological parameters) this site also has is two actinic flux spectroradiometers system for measurement of solar actinic flux and the determination of 23 important atmospheric photolysis reactions. The UH-Moody Tower facility is also part of the USDA UV-B Monitoring Network, the NASA Aerosol Robotic Network (AERONET) and the EPA/NOAA Brewer Network. As such, UH has a suite of UV and visible irradiance instruments, including an Ultraviolet Multifilter Rotating Shadowband Radiometer (UV-MFR-7) and a MFR-7 to measure the total and diffuse downwelling irradiance at multiple wavelengths. These instruments will be used to calculate aerosol optical depths during cloud-free conditions. UH will deploy a Total Sky Imager to capture hemispheric digital images of the cloud fraction, a CIMEL sun photometer to measure the aerosol optical depth at multiple VIS and IR wavelengths, and a Brewer Mark IV (Sci-Tech) for spectral measurements of UV direct beam and global irradiance. In conjunction with the TUV radiative transfer (RT) model, the data from this spectrally-resolved radiation package will be used to determine the aerosol SSA and the overhead ozone column. The TUV model will also be run with “background” aerosol profiles with standard optical properties to calculate “cloud-free” photolysis frequencies. Photochemical box models will be run with both measured and modeled cloud-free photolysis frequencies to investigate the impact of Houston’s aerosols on photochemical cycling.

Expected Results:

The relationships between aerosols, ozone, clouds on surface UV radiation learned from this project should be applicable to other U.S. cities. An understanding of the impact of aerosols on photochemistry of Houston is important to for improving the air quality, and quality of life for the 2.5 million residents of Houston and the estimated 5 million in the Houston metropolitan area.. This project will generate a unique dataset that may be used by other researchers to investigate the relationships between pollution, total column ozone, and surface UV-B levels.

Publications and Presentations:

Publications have been submitted on this project: View all 16 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 11 journal articles for this project

Supplemental Keywords:

EPA Region 6,

Progress and Final Reports:

  • 2007 Progress Report
  • 2008 Progress Report
  • Final