Air quality in Houston

What is the air quality in Houston?

In recent years, Houston’s average annual air quality index (AQI) score has met the US Environmental Protection Agency (EPA) qualifications for “good,” indicating that the air generally poses little to no risk to health. Annual averages, however, can smooth over elevated periods of pollution and fail to portray potential risks accurately. Despite an annual “good” AQI, there have been a number of unhealthy pollution days in recent years. These short-term pollution events have caused Houston to fail to meet federal attainment levels for daily ozone since monitoring began two decades ago.

An AQI value is calculated by weighting six criteria pollutants for their risk to health in a formula. The pollutant with the highest individual AQI dictates the overall AQI score. Due to the prevalence and relative danger of inhaling fine particulate matter (PM2.5) and ozone, these two pollutants most often determine overall AQI.

PM2.5 pollution describes a mix of fine airborne particulate matter measuring 2.5 micrograms or smaller in diameter. Due to its near microscopic size, PM2.5 is able to penetrate deep into the lungs and then into the bloodstream, potentially causing a wide range of short- and long-term health effects. Exposure to PM2.5 has been directly linked to conditions including heart and lung disease and early death.

In 2019, Houston met the US EPA standard for annual PM2.5 exposure (12 μg/m³) but exceeded the more stringent World Health Organization standard (10 μg/m³) by 0.8 μg/m³.

November (14.8 μg/m³), December (13 μg/m³), and March (12.7 μg/m³) of 2019 all experienced particle pollution levels defined as US AQI “moderate” – air that poses some risk to sensitive groups, including children, the elderly, and people with pre-existing cardiovascular or respiratory health conditions. While “moderate” PM2.5 levels are not uncommon in the Houston area, Harris County averages just 1 day a year of air quality deemed “unhealthy for sensitive groups.”

The Environmental Defense Fund and the Harvard School of Public Health estimated that Houston’s PM2.5 pollution, however moderate, contributed to more than 5,000 premature deaths and cost $49 billion in economic damages in 2015 alone.¹ Such high annual costs highlight a need to further tighten PM2.5 standards. A study conducted by the US EPA estimated that reducing the federal limit for annual PM2.5 from 12 μg/m³ to 9 μg/m³ could save as many as 12,150 lives a year (neighboring Canada uses a PM2.5 standard of 8 μg/m³).²

Ozone is another pollutant of concern in Houston. Ozone is a gaseous pollutant and component of smog formed in the atmosphere when sunlight causes nitrogen oxides (NO₂) and organic substances (VOCs) to react. Like PM2.5, ozone can also cause respiratory infections, inflammation, and premature death.

According to the 2019 State of the Air report by the American Lung Association (ALA), Houston ranks 9th nationally for worst ozone pollution with a weighted average of 22.3 days annually exceeding standards.³

Houston’s relatively high average temperatures, abundant sunshine, large oil and gas industry, and dispersed population reliant on motor vehicles for transport all make it challenging for the city to reach attainment levels. The city has never, in fact, met daily attainment levels for ozone. Other urban Texas cities, such as Dallas, Fort Worth, Austin and San Antonio, are in a similar position, having never met federal ozone levels.

Air quality data changes hourly based on emissions and weather. Check real-time air quality levels in Houston at the top of this page and follow Houston’s forecast air quality data to take proactive steps in reducing your exposure to unhealthy air.

Has air quality improved in Houston?

Like much of the United States, Houston’s air pollution has improved over recent decades as a result of increasingly stringent regulations on a wide variety of industries. Just twenty years ago, Houston often swapped ‘most polluted’ titles with Los Angeles. Today, Houston’s air quality is much improved, though still relatively high compared to the US average. According to the 2019 World Air Quality Report, Houston ranks 244th out of 1517 included cities for highest PM2.5 in the United States. Moreover, the city has seen a recent rise in both PM2.5 and ozone pollution since 2017.

For fine particulate matter, or PM2.5, Houston experienced a 7.8 percent increase from 2017 to 2018 and another 11.3 percent increase from 2018 to 2019. These increases, though subtle, show a concerning trend. Many blame these increases on Houston's growing population and economy. These reasons, however, do not necessarily entail increased emissions. Shifting towards cleaner energy and more fuel-efficient low emission vehicles represent two impactful means for further reducing Houston air pollution levels.

For ozone, Houston experienced its highest levels between 1997 and 1999, with a weighted average of 110 unhealthy air days per year. This number has fallen dramatically since – yet, the most recent average of 26.7 days is still almost 8 times the US EPA attainment limit allowing no more than 3.2 unhealthy ozone days per year.

‘Stay-at-home’ measures implemented during the 2020 COVID-19 pandemic resulted in some city-wide pollution reductions, including a 13 percent drop in ozone.⁴ As the economy opened back up, however, pollution reductions diminished. While short-lived, lockdown measures suggest that reductions are possible if more residents transitioned to zero-emission electric vehicles and industry relied on a greater share of renewable energy.

Why does Houston have unhealthy air quality?

Houston’s unhealthy air quality is primarily attributable to ozone pollution. Warm urban climates are naturally predisposed to higher ozone levels because they provide ideal environmental conditions for ozone formation, such as sunshine, heat, and abundant precursor pollutants.

Like most big cities, air pollution seems an inevitable byproduct of the area’s population and economy. There are 7 million people, 5 million registered vehicles, and 121,000 industrial businesses in the greater Houston area. The Port of Houston is one of the nation's busiest, producing 4.1 tons of smog-forming pollution each year.⁵

In addition to these emission contributors, global warming is expected to exacerbate ozone levels by providing warmer temperatures that accelerate ozone formation.

60 percent of Houston’s ozone pollution is estimated to result from vehicle exhaust alone. During the COVID-19 pandemic, ‘stay-at-home’ measures are likely to have contributed to the city’s improved air quality by keeping cars off the road in significant numbers. Houston saw a 13 percent reduction in ozone during this time.

Houston neighborhoods of higher density tend to have higher pollution levels. Downtown Houston AQI, for example, tends to be much higher than in the greater Houston area. Use the air pollution map of Houston to understand local variances across the city.

What is Houston doing to control air pollution?

Air pollution is largely an unwanted byproduct of our mobile, consumerist lifestyles. Advancements in green technology, renewable energies, and air pollution filtration as well as increasingly stringent regulations all offer opportunities to greatly reduce our environmental impact with few changes to our lifestyle.

Current efforts to curb air pollution in Houston include:^6,7

• specialized fuel requirements
• inspection programs and permit systems
• construction bans and permitting
• emission caps and budgets
• improvements to the desirability and accessibility of public transport
• incentives and infrastructure for zero-emission electric vehicles

In 2020, the city of Houston and the Harris County and Environmental Defense Fund (EDF), with support from Houston Endowment, committed $1.1 million dollars to growing Houston’s air quality monitoring network in order to help identify the facilities pose the greatest health risks.⁸ The new effort follows after a series of industrial fires and explosions exposed gaps in air quality monitoring and accountability, including a fire at the Intercontinental Terminals Company (ITC) in Deer Park in March 2019. Increasing Houston air quality data granularity is an important step towards both responding more effectively to emergency situations involving unhealthy pollution spikes and holding high-emitting industries accountable for excess emissions.

Where is air pollution in Houston the worst?

In Houston, tackling air pollution is an environmental justice issue. 75 percent of the health burden is carried by communities who exceed the current federal PM2.5 standard, usually at no fault of their own. Pollution-emitting city features like airports, major roadways, factories, industrial complexes, and power plants are all historically located near disadvantaged communities. These communities are often disproportionately home to people of color, those with fewer financial resources and political power, and those with chronic health conditions.

Houston’s Fifth Ward is one such example of a neighborhood with high-polluting industries, including several metal recyclers and concrete processing plants, along with disproportionately non-white (90 percent) and impoverished (40 percent below federal poverty line) residents.⁹ NO₂ levels here are 48 percent higher than the rest of the city, and residents disproportionately suffer from related health effects in comparison to greater Harris County, such as:

• Asthma: 11 percent (Harris County: 9 percent)
• Chronic Obstructive Pulmonary Disease (COPD): 10 percent (Harris County: 6 percent)
• Coronary Heart Disease: 9 percent (Harris County: 5 percent)
• Stroke: 6 percent (Harris County: 3 percent)
• Life expectancy: 69 years (Harris County: 78 years)

Houston’s more affluent River Oaks neighborhood, by contrast, has no industrial pollution sources, lower pollution levels, and fewer rates of pollution-related health impacts. Residents here have asthma rates of 7 percent, COPD rates of 4 percent, stroke rates of 2 percent, and live to 85 years on average.

Use IQAir’s Houston air quality map to discover how pollution levels vary across the city. When pollution levels are currently or forecast to be high, follow the recommended health guidelines in order to reduce your exposure.

+ Article Resources

[1] Roy A. (2020, May 11). Amid COVID-19, the Trump administration sets dangerous air pollution standards. What is at stake for Houstonians? Environmental Defense Fund.
[2] Environmental Protection Agency. (2019). Policy assessment for the review of the national ambient air quality standards for particulate matter, external review.
[3] American Lung Association. (2019). State of the Air – 2019.
[4] Rogalski J. (April 10, 2020). A side effect of COVID-19 crisis: Houston's air is cleaner. WQAD 8.
[5] Environmental Defense Fund. (2020). Cleaner air in port cities.
[6] Green K, et al. (2000, November 1). Clearing the air in Houston. Reason Foundation.
[7] City of Houston. (2020). Fleet management department - electric vehicles.
[8] Environmental Defense Fund. (2020, September 28). New multi-agency effort aims to reduce air pollution, disaster risk in Houston.
[9] Environmental Defense Fund. (2020, June 3). Finding pollution—and who it impacts most—in Houston.