Particulate matter (PM, also known as aerosol) consists of very small solid or liquid materials distributed in a background gas. Levels of atmospheric PM have been correlated positively to rates of illness and premature death among the exposed populations based on the mass concentration of all particles that have diameters smaller than 2.5 millionths of a meter (PM2.5). However, increasing evidence indicates that the smallest particles (generally in the range of a few to 100 billionths of a meter in diameter), which typically contribute very little to the particulate mass concentration but very strongly to the overall particulate number concentration (i.e., how many individual particles are present), have profound implications for exposed populations because they are small enough to cross tissue boundaries and enter the blood stream directly. Therefore, a continuous, high-quality, high time-resolution data set of particle number concentration in an urban area known to suffer from poor air quality will be highly valuable. Generation of such a one-year data set in Houston is the primary objective of this project.
The generation of this data set will be achieved through use of commercially available instrumentation known as a condensation particle counter (CPC). A CPC operates by exposing particles in an ambient sample to saturated water vapor and then cooling the sample down so that the water condenses onto the particles and makes them large enough to be detected by a laser. Based on the frequency of detection of particles by the laser and air flow rate through the CPC, a number concentration (# of particles/volume of air) can be determined. Typical particle number concentrations are on the order of thousands of particles per cubic centimeter of air.
The CPC will be deployed at the air quality monitoring station located atop the North Moody Tower on the University of Houston main campus. The planned date for initial deployment is February 1, 2012, and measurements will be taken for one calendar year at a frequency of one minute. This location is ideal for air quality measurements as it is influenced by many local and regional air pollutant sources, including power generation facilities, highways, airports, and the industrial facilities associated with the Houston Ship Channel. Deployment at this location provides a wealth of complementary data (meteorology, other air pollutants, etc.) that will be invaluable to the initial assessment and analysis of the particle number concentration data. After quality checks are complete, data analysis techniques, performed in conjunction with statisticians, will focus on methods for determination of factors that control particle number concentrations in Houston. Data will be made available publically.
The project addresses a threat to sustainability of clean air because appropriate control strategies cannot be derived without knowledge of present day concentrations and sources; in this case, the data collected may provide the basis for future legislation. This project also addresses concerns beyond air quality because PM deposits to surface waters (thereby affecting water quality) and because PM affects the amount of radiation reaching the Earth’s surface (thereby participating in climate forcing). Results will be presented at a national conference (American Association for Aerosol Research (AAAR) to be held in Minneapolis, MN, in October 2012). At the end of the project, a manuscript describing data collection and analysis will be submitted to a peer-reviewed scientific journal for publication.
Publications & Outcomes:
A.P. Rutter, K.M.
Shakya, R. Lehr, J.J. Schauer, and R.J. Griffin, Oxidation of gaseous elemental
mercury in the presence of secondary organic aerosol formation, Atmos.
Environ., 59, 86-92, 2012. (publication)
Y.J. Leong, C. Gutierrez, R.J. Griffin, and B.L. Lefer,
Measurement of aerosol number concentrations in Houston, TX, American
Association for Aerosol Research Annual Conference, Minneapolis, MN,
October 2012. (poster)