Air quality changes in Houston, Texas, during the COVID-19 shutdown period in spring 2020
Abstract
We downloaded and analyzed a large set of air quality data from the State of Texas air quality monitor network in Harris County, Texas. Continuous hourly measurements of NOx, CO, and hydrocarbons from automated gas-chromatographs were maintained throughout the initial "stay-at-home" period, which began on 20 March and lasted through the end of May 2020. We focused our attention on NOx measurements from monitors located in different urban Houston locations, and on hydrocarbon and NOx measurements located at sites in east Houston affected by petrochemical industry emissions along the Houston Ship Channel. As expected from previously published satellite data, we found that near-surface NOx levels, compared between 4-week periods before and after the "shutdown", decreased substantially. However, the decrease was far from uniform. The largest drops occurred at a monitor located next to busy interstate 610, which tends to display high NOx levels due to its nearness to dense car traffic. However, negligible drops occurred at comparatively lower NOx, residential sites away from highways, suggesting that either neighborhood car traffic, in contrast to highway traffic, probably did not decrease by similar margins, or that car traffic represents a minor NOx source in these neighborhoods.
Combination analyses of NOx and hydrocarbons using factor analysis and non-negative matrix factorization reveals that reductions in car traffic are the far dominant reason for lower NOx and hydrocarbon levels. Industrial emission sources did not seem to be strongly affected by the "shutdown", but played a larger relative role in air quality due to the reductions in on-road emissions. This reflected a unique air quality situation by selectively reducing a large single source of NOx and a subset of hydrocarbons associated with tailpipe and evaporative emissions. This is akin to replacing a large set of on-road gasoline vehicles with electric cars, meaning the air quality levels during the shutdown may have provided a glimpse of the future under mostly electrified urban transport.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMA067.0006S
- Keywords:
-
- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0345 Pollution: urban and regional;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0240 Public health;
- GEOHEALTH