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Friday, April 24, 2020

Effects of Pandemic on Air Quality

Has air quality improved?

HARC provides an in-depth analysis of COVID-19 and its impact on air quality.

COVID-19 has impacted every facet of life. At HARC, our research goals are to provide scientific analysis on how the pandemic, social distance measures, and changes in daily behavior continue to effect environmental, societal and economic outcomes. The results are featured here on our blog, through social media, and the HARC website.

Visit our Research Project page to learn more about the ongoing COVID-19 analyses.

Air Quality – What Matters?

Changes in air quality are most effectively assessed by analyzing multiple pollutants at various locations over time. While ozone levels are important and positive impacts have been reported, HARC’s analysis addresses additional levels of pollutants including nitrogen oxides (NOx) and the BTEX air toxics.  Future studies will examine particulate matter less than 2.5 micrometers in diameter (PM2.5), All these air pollutants present serious risks to human health and well-being and are especially problematic from a respiratory, cardiovascular, and nervous system perspective. Some BTEX gases are also known carcinogens (cancer causing).

Ground level ozone (O3) is a secondary air pollutant formed by the chemical reaction between VOCs and NOx in the presence of sunlight. High levels of ozone can be caused by elevated emissions of VOCs and NOx, especially when coupled with weather conditions characterized by abundant sun and heat that facilitate the photochemical process associated with ozone formation. Like nitrogen dioxide and PM2.5, ozone is one of the primary criteria air pollutants for which a National Ambient Air Quality Standard (NAAQS) exists.

NOx refers to a group of highly reactive and harmful air pollutants that are comprised of nitric oxide (NO) and nitrogen dioxide (NO2), a regulated criteria pollutant with a NAAQS.  NOx is primarily produced during fuel combustion processes, mainly those associated with motor vehicles, traditional fossil-fuel based power generation, and industrial processes. Although local transportation-related sources of air pollution have decreased dramatically in recent weeks, local weather patterns and air chemistry are still important drivers of air quality.

BTEX refers to a group of volatile organic compounds (or VOCs) made up of benzene, toluene, ethylbenzene, and xylenes. The primary sources of BTEX emissions are refineries, petrochemical plants, vehicle emissions, and evaporative losses from fuel storage tanks. While BTEX compounds are constituents of a suite of Hazardous Air Pollutants (HAPs), also referred to as toxic air pollutants or air toxics, regulated by the US Environmental Protection Agency, no NAAQS exists for them and other HAPs.

From Here to There – a Regional Analysis

Data from across the region, across the state, and across the nation were analyzed to provide a comprehensive report on the pandemic’s impact on air quality.

For Ozone analysis: Analyses were undertaken for six Texas metro areas and 16 counties by averaging 20 stations within the Houston-Galveston area, 52 stations across Texas and 145 stations across the nation. The data were collected from the EPA's AirNow database.

For NOx analysis: Hourly concentration data were collected by the Texas Commission on Environmental Quality (TCEQ) Continuous Ambient Monitoring Station (CAMS) network. Data were retrieved for six stations around the Houston Ship Channel area and three additional stations across Harris County.

For the BTEX analysis: The daily average of hourly aggregated concentrations of Benzene, Toluene, Ethylbenzene, and Xylene across six stations in the Houston Ship Channel were calculated. The data were collected by TCEQ’s Automated Gas Chromatograph (AutoGCs) monitoring network.

Timing is key
Air quality data retrieved from a period of time prior to the COVID-19 outbreak (March 11 through April 13, 2014-2019) were used as a comparative baseline to assess air quality for the period from March 11 through April 13, 2020 (during the COVID-19 outbreak). Analyses were focused on a weekday, weekly, and monthly basis.

The air quality analysis was led by Dr. Mustapha Beydoun, HARC’s Vice President, Dr. Meredith Jennings, a Postdoctoral Research Scientist in Community Resilience, and Dr. Ebrahim Eslami, Post-Doctoral Research Scientist in Air Quality. Researchers at HARC are analyzing data describing regional air quality and mobility to determine the extent of regional and statewide changes due to COVID-19 and the resulting stay-at-home orders. In the coming weeks, HARC will work to gather and share this information broadly. Please visit the project web page, follow us on social media, and subscribe to our newsletter to learn more.