Influence of local and global sources on atmospheric particle concentrations in Houston, Texas

Thursday, February 17, 2011

6:15 pm
125 Hudson Hall, Duke University


Shankar Chellam

Shankar Chellam, Ph.D.
Professor University of Houston, Texas
Department of Civil and Environmental Engineering and the Department of Chemical & Biomolecular Engineering

Abstract: Atmospheric particles originate directly from natural sources and human activities (primary particles) or condense from gaseous precursors (secondary formation). Sources of primary particles include industrial activity, combustion of biomass, coal, and oil, motor vehicles, resuspension of crustal material, etc. In addition to these local sources, trade winds carry a portion of the 160 to 760 teragrams of dust emitted from the Sahara-Sahel region in North Africa to the continental United States. This presentation focuses on our research quantifying (i) contributions of petroleum refineries to ambient airborne particulate matter levels during "routine" operations, and (ii) transient variations in aerosol concentrations in the greater Houston area caused by fluidized bed catalytic cracking unit malfunctions and incursion of aeolian North African dust.

Novel dynamic reaction cell inductively coupled plasma – mass spectrometry (DRC-ICP-MS) methods were developed to measure a wide range of main group, transition, and lanthanoid elements in atmospheric particulate matter. These analytical techniques were used to measure over 40 elements in PM2.5 and PM10 samples collected from the proximity of oil refineries and from a residential area to estimate the contributions of fluidized‐bed catalytic cracking operations to ambient particulate matter.

Cat cracking operations primarily contributed to lanthanoid enrichment in fine PM even though they comprised only 2% of the apportioned mass during routine operation. Significantly different results were obtained during a reported short-lived emission event, which we estimated to increase cat cracking contributions by a factor of 30 – 100. Importantly, refinery emissions was tracked to a site approximately 50 km downwind from the source, illustrating the potential exposure of humans over a large geographical area through the long‐range transport of atmospheric fine particles. We have also measured and monitored an unreported, transient anthropogenic particulate matter emission episode which contributed to higher particulate matter levels in Houston, Texas. The presentation will conclude with our investigations of a particular North African dust episode, which increased aerosol concentrations in Houston over a 3-day period from July 25 – 27 in 2008.

Based on our findings, we recommend long-term independent monitoring of aerosols and trace elemental speciation especially in industrial areas. This would be particularly useful towards air quality management efforts as well as providing data to better evaluate the metals hypothesis for adverse health effects associated with airborne particles.