Air quality in Phoenix

What is the air quality in Phoenix now?

Phoenix is the capital and most populous city in Arizona. In 2019 it had an estimated population of almost 1.7 million people.

With numbers such as these, it comes as no surprise that it is the fifth most populous city in the entire US and the only state capital with a population in excess of 1 million.

It is located at the confluence of the Gila and Salt Rivers and was first recognised as a city in 1889. Despite its hot desert-like climate, Phoenix had developed an excellent canal and irrigation system which enabled agricultural-based industries to flourish.

In early 2021, Phoenix was enjoying a period of “Good” quality air with a US AQI reading of just 36. This classification is in line with the recommendation from the World Health Organisation (WHO). The recorded level of the pollutants was as follows: PM2.5 - 5 µg/m³, PM10 - 18.9 µg/m³ and ozone (O₃) - 89 µg/m³. The numbers are stated in micrograms per cubic metre.

With a level as low as this, doors and windows can be opened to allow some fresh air inside and all types of outdoor activity can be enjoyed without fear.

Phoenix’s air quality on average is rated an air quality index (AQI) score of less than 50, or “good.” Despite Phoenix's clean air quality on annual and monthly averages, the city still experiences a number of unhealthy ozone and PM2.5 days. From 2016 to 2018, there was a weighted average of 46.5 days of unhealthy air.¹ These pollution days resulted in Phoenix failing air pollution attainment for ozone and PM2.5.

Is the air quality in Phoenix the same throughout the year?

Looking back at the figures released on the IQAir website, it can be seen that there is only a slight variation in the records. It would appear that December is the worst month with a recorded figure of 14.5 µg/m³ which classifies it as being “Moderate” with figures between 12.1 and 35.4 µg/m³. The months of November and January saw an improvement with better figures between 10 and 12 µg/m³. The remaining 9 months of the year saw Phoenix attain the target figure of 10 µg/m³ or less by the WHO.

Taking into account the figure from the last four years, it is seen that the air quality is remaining fairly constant. In 2017 the figure was 8.4 µg/m³ followed by 8.6 in 2018. 2019 saw a very good figure of just 5.6 µg/m³ before it slipped back to 8.4 µg/m³ in 2020.

Phoenix tends to experience cleaner air in the summer and more polluted air in the winter.

Temperature inversions in the winter largely contribute to these months having 2.5 times higher AQI than in the summer months. On average, May and June are Phoenix's cleanest months annually, whilst November and December are the most polluted.

The greatest challenge to Phoenix air quality is ozone pollution. Ozone is a gas pollutant formed when nitrogen oxides and organic substances react under sunlight. Since ozone is not released directly but rather formed in the atmosphere from other pollutants, it is often considered a difficult pollutant to control.

Abundant sunlight and heat as a requirement for ozone formation mean that Phoenix ozone levels tend to be worse in the summer than in the winter (an opposite trend from Phoenix average pollution levels and PM2.5 levels). In 2019, unhealthy ozone levels only occurred between the dates of 3^rd May and 13^th September. Historically, ozone levels are always in the “green” healthy category during the winter months.

According to the State of the Air report published by the American Lung Association, Maricopa County, of which Phoenix is the county seat, was rated an “F” and ranked 7^thamong 228 included metropolitan areas for high ozone days. From 2016 to 2018, there was a weighted average of 39.8 days that were deemed unhealthy for ozone alone.

What are the main industries in Phoenix?

Some of Phoenix’s industrial manufacturing units include aircraft parts, electronic equipment, agricultural chemicals, radios, air-conditioning equipment and leather goods.

Tourism normally plays a vital role in the local economy but like so many other destinations, Arizona saw a lot fewer tourists in 2020 due to the COVID-19 pandemic.

Is the air in Phoenix highly polluted?

In 2020, Phoenix was ranked as having some of the worst air quality in the country in the American Lung Association's State of the Air report. The city ranked 7^th for year-round particle pollution. They also ranked Phoenix as 10^th for short-term particle pollution.

The American Lung Association produces a new report on an annual basis called the “State of the Air”. It found that the majority of American cities with the worst air pollution had been in the West. The changing and warming climate plays a big role in this trend. The past five years have been some of the warmest years on record globally, so those extreme temperatures, together with droughts, wildfires, certainly add to increased particle pollution.

Over the past few months, however, air quality has improved significantly with more people staying at home and driving less due to COVID-19 restrictions. Although this may be temporary, it’s an indication of what it could be like if more people committed to cleaner fuels and working from home.

While Phoenix continues to struggle to meet current ozone standards, many health experts are proponents for further lowering the federal standard. They advocate that current regulations limiting ozone levels to no more than 70 ppb do not sufficiently safeguard the most vulnerable populations for adverse health effects.² In order for Phoenix to meet current standards and strive for even lower levels, the city must focus on its greatest ozone contributor: transportation.

Phoenix live air quality data is available at the top of this page. Follow Phoenix forecast air quality data and the posted health advisories to take action against pollution levels and reduce your pollution exposure.

What are the chief sources of pollution in Phoenix?

Phoenix, along with much of the United States, experienced significant air quality improvements since the Clean Air Act of 1970 and later 1990 amendments.

In recent years, however, Phoenix air quality has been on the decline for both PM2.5 and ozone pollution. 2019 was an exception to this trend, showing improvements as compared to both 2018 and 2017.

Data from the federal Environmental Protection Agency (EPA) and Arizona Department of Environmental Quality (ADEQ) show that most air pollution comes from vehicle emissions while pollution from non-vehicle sources has declined dramatically since the 1990s.

Even with a decrease in ozone pollution in 2019, ozone levels still pose significant risks to Phoenix residents. Limiting ozone levels in the future relies primarily on reducing auto emissions rather than emissions from Phoenix’s relatively small manufacturing sector.³ Transportation emissions can be further reduced by shifting to more fuel-efficient, low emission vehicles and making public transportation more accessible and attractive.

According to a study by the South West Energy Efficiency Project (SWEEP), moving to electric vehicles could greatly reduce Arizona air pollution levels, with reductions in nitrogen oxide (a key precursor pollutant for ozone formation) levels by up to 76 per cent, and PM2.5 levels by up to 60 per cent.⁴

Legislation is currently being considered which would compel energy providers to provide 50 per cent of their energy from sustainable/renewable sources before 2030. This will not be popular with the utility companies who warn of increases in prices which will have to be passed on to the consumer.

The state of Arizona is already a leader in the renewable energy sector and is nationally ranked as 3^rd when considering installed solar capacity. The local trade body lists Arizona as already providing 50 per cent of its energy from renewable sources.

One of Arizona’s main energy supplier has reported that they have reduced their carbon dioxide emissions by 14 per cent because of their diversification policies. It is noteworthy, however, that the continued increase of carbon dioxide is due to vehicle emissions and not from power stations.

Can the quality of Phoenix’s air be improved?

By the year 2050, Phoenix intends to have the best quality air both for its human population as well as for the environment. The standards laid down are that the air quality has to be excellent on at least 90 per cent of the days. At the moment, Phoenix achieves between 70 and 80 per cent of good or excellent visibility days.

They are already committed to reducing ozone and dust particulate pollution. Transit, light rail, cycle paths, and pedestrian-friendly areas reduce vehicle emissions and promote land use planning and urban designs for a more sustainable and vehicle-free environment.

They already have what is considered to be a pioneering dust control program for the city of Phoenix. It includes asphalt treatment for roads, hard shoulders, alleys and city-owned parking lots as well as anti-trespass laws to establish dust control methods for underdeveloped land or vacant lots.

What part do temperature inversions play in Phoenix’s poor quality air?

The accumulation of air pollution in Phoenix during the winter, for example, is primarily the result of temperature inversions. In normal conditions, the sun heats the ground creating warmer air near the ground’s surface and cooler air just above. In these conditions, polluted ground-level air is able to rise and disperse over large areas.

During a temperature inversion, generally occurring in the winter, weak sunlight and colder conditions create colder ground-level air and warmer air above. When this happens, the cold polluted air near the surface is trapped or prevented from rising due to the warm air above. The result is the accumulation of pollution over time as emissions remain relatively constant, often creating a ‘brown haze’ over the horizon.

Local winds can further exacerbate this effect by moving pollution across different parts of the valley.⁵ During the day, pollution spreads more freely across the valley, moving up the mountains and to the surrounding Phoenix metropolitan area. At night, as temperatures drop, cold air flows from the mountains to the south, settling in the lowest point of the valley. This moving air contains pollutants from the surrounding area, concentrating them near the southern part of the Salt River and west Phoenix.

When a temperature inversion is in place, only rain or wind can diffuse the cold, polluted air. Heat and sunlight during the afternoon can end an inversion, allowing pollution to disperse, but in the winter, inversions frequently occur again a few hours after dusk.

Warming summer temperatures as a result of global warming may be worsening Phoenix's ozone problem by creating more ideal conditions for ozone formation. Between 1980 and 2015, state-wide temperatures have risen from an average of 71.3°F to 75.5°F.⁶ Phoenix is the fourth fastest-warming city in the United States.

Phoenix AQI varies across the city and is usually higher near major roadways. In the winter, west Phoenix often shows slightly higher air quality levels as a result of seasonal weather effects. Use the Phoenix air pollution map to observe the impact of local emission sources on real-time air quality levels, and compare air quality levels to Tucson, Arizona’s second most polluted city after Phoenix.

What are the health implications of breathing Phoenix’s polluted air?

Many residents experience some type of symptoms related to air pollution, such as watery eyes, coughing or noise when breathing. Even for healthy people, polluted air can cause irritation or breathing difficulties during exercise or outdoor activities. Your actual risk depends on your current health, the type and concentration of the pollutant, and the length of time you have been exposed to the polluted air.

Some people are more likely to be affected by polluted air than others. These include people with pre-existing respiratory problems such as those with heart and lung disease.

People who experience difficulty when breathing, often suffer from asthma attacks or emphysema.

Pregnant women and children under the age of 14 are also more susceptible, as are people who need to work outside for long hours each day.

Athletes who exercise strenuously on a regular basis need to take extra precautions when the air quality is poor.

+ Article Resources
[1] American Lung Association. (2019). State of the air – 2019.
[2] BMJ. (2020, February 10). Daily exposure to ozone pollution linked to increased risk of death.
[3] Francis S. (2019, October 27). Arizona's air quality is getting worse and making people sick. Here's how we solve it.
[4] Salisbury M. (2013) Air quality and economic benefits of electric vehicles in Arizona.
[5] Stone E. (2019, December 31,). Winter air really is worse in south, west Phoenix. Here's why.
[6] Climate Central. (2019). American warming: The fastest-warming cities and states in the U.S.