Air quality in Washington, D.C.

What is the air quality in Washington, D.C.?

Washington, D.C.’s air quality suffers from high ozone levels, which exceed government standards. The city, however, meets federal attainment for all other key criteria pollutants monitored by the US Environmental Protection Agency (EPA): PM2.5, PM10, CO, SO₂, and NO₂.

Ozone is an invisible, highly reactive gas molecule composed of three oxygen atoms. Rather than being directly emitted into our air by industrial activity, motor engines, or various sources of combustion, like other criteria pollutants, ozone is formed in our atmosphere from airborne hydrocarbons and nitrogen oxides reacting in sunlight. This property of forming from precursor pollutants in the air rather than ground-based activity makes ozone difficult to manage. Precursor pollutants may originate from local emission sources or flow into a city from up to a thousand miles away.

Breathing ozone pollution can cause serious health complications, ranging from a cough and breathing problems to respiratory infections, cardiovascular effects, and premature death.

The District of Columbia has failed to meet ozone attainment levels since at least 1996.¹ Several years ago, the city got close, however, with a weighted average of 3.3 unhealthy ozone days from 2014-2016, just slightly above the 3.2-day limit for unhealthy days. Since this period, Washington, D.C.’s ozone levels have been on the rise. From 2016 to 2018, the most recent monitoring period, the city experienced 5.2 unhealthy ozone days. These days in excess of safe ozone levels have landed the city an “F” rating for ozone levels since tracking began.

A study conducted by the Ozone Transport Commission estimated that roughly 24,448 residents experienced acute respiratory symptoms in 2018 as a result of high ozone levels, while 19 were admitted to the hospital for severe symptoms.² Warming temperatures as a result of climate change are expected to increase ozone levels as a result of hotter, more ideal conditions for ozone formation. To combat this, increased regulation on heavy duty trucks and vehicles as well as improved regional cooperation with nearby Virginia and Maryland is critical to further reducing ozone levels in the future in the wake of rising temperatures.

Fine particulate matter, or PM2.5, is another closely monitored and actively managed pollutant in Washington, D.C. PM2.5 describes any airborne particulate matter smaller than 2.5 microns in size, including a wide range of chemical makeups and sources. Its near microscopic size enables PM2.5 to be inhaled deep into the lungs and often into the bloodstream. This property contributes to PM2.5’s far reaching health implications, including short-term effects like coughing, wheezing, shortness of breath, and aggravated asthma as well as long-term effects like lung damage and decreased lung function, cancer, and premature mortality.³

Though Washington, D.C., has met federal attainment levels for annual and 24-hour PM2.5 since 2009, pollution events are not uncommon, particularly during the winter months. December, January, and February are often Washington, D.C.’s most polluted months for PM2.5. During these months, increased emissions from home and building heating can become trapped by temperature inversions, a weather event in which a hot layer of air traps cooler, more polluted ground-level air from rising and dispersing. In 2017, October, November and December all experienced average PM2.5 levels in the “moderate” US AQI category, outside of the federal target.

Follow live air quality data in Washington, D.C., at the top of this page and on the IQAir air pollution app. Use the District of Colombia forecast air quality data to plan ahead and take precautionary measures to reduce your pollution exposure.

How polluted is the air quality in Washington, D.C.?

From a long-term perspective, air quality in Washington, D.C., has seen drastic improvements over recent decades. Data from the EPA National Emissions Inventory (NEI) estimates that emissions of all criteria pollutants and their precursors have gradually fallen since 1996. These reductions come despite increases in population, employment, and households, suggesting that actions taken to control Washington, D.C.’s air pollution have generally been successful.

Air quality levels in Washington, D.C., are notably lower than neighboring cities. This has been true for ozone levels since 2002 and PM2.5 levels since 2008.² Air pollution levels in nearby Baltimore, for example, are consistently worse, on average, than Washington, D.C. Polluted air blown from Maryland and Virginia contribute significant amounts of pollution to the D.C. area. Cooperating with neighboring states to implement further legislation on emissions presents an opportunity for further reducing air pollution in the District.

Air quality levels in Washington, D.C., fell by 10 to 20 percent during the 2020 COVID-19 lockdown compared to the same time period a year prior in 2019.⁴ City lockdown measures shuttered nonessential businesses and resulted in greatly reduced traffic congestion, as residents tended to avoid non-essential travel. These reductions highlight what could be achieved through transitioning residents to greener transport options and more fuel efficient, lower-emission vehicles.

In recent years, Washington, D.C., has taken steps to improve the attractiveness and accessibility of green transport options like walking and biking, which reduce car traffic and lead to cleaner air in the district. This strategy has included adding many more miles of bike lanes, instituting “slow streets” that limit vehicle speeds to 15 mph, and growing the network of city sidewalks.

Does Washington, D.C., have good air quality?

Washington, D.C., unhealthy air quality is the result of elevated ozone levels. As an urban area with relatively little industry, the majority of Washington, D.C., air pollution comes from vehicular emissions and emissions blowing in from neighboring cities and states.

Nearly half of Washington, D.C., air pollution originates from mobile sources: cars, trucks, trains, and planes. On-the-road mobile emissions are the largest source of the ozone precursor nitrogen dioxide (NOx) and the second largest source of the ozone precursor volatile organic compounds (VOCs).²

Regionally, most precursor pollutants for ozone formation originate in the areas surrounding Washington, D.C. Maryland is estimated to contribute to 52% of the region’s VOCs and 47% of the region’s NOx, while Virginia contributes 43% of the VOCs and 45% of the NOx. Washington, D.C., on the other hand, is estimated to only contribute 5% of the region’s VOCs and 8% of the region’s NOx.

Washington, D.C., AQI can vary from location to location, even within the city. Use the Washington, D.C., air pollution map to understand the flow of emissions from neighboring cities and local sources.

What are recent levels of air pollution in Washington, D.C.?

In the early period of 2021, Washington, D.C., was seen to have a variety of different PM2.5 readings, recorded over the course of March. These ranged from lows of 2.1 μg/m³ all the way up to highs of 20.9 μg/m³ taken over the course of the month. Whilst a majority of the readings fell within the World Health Organizations (WHO's) target goal of 10 μg/m³ or less, it still stands to reason that with spikes going up to 20 μg/m³ and above, the citizens of Washington D.C. still have many pollution-related issues to deal with, even during the Covid-19 era which has seen massive reductions in anthropogenic movement and all related activity (although many industrial processes and shipping via land, sea and air have not ceased).

This high of 20.9 μg/m³ would place Washington, D.C., in that particular time frame into the ‘moderate’ pollution ratings bracket, which needs a PM2.5 reading of 12.1 to 35.4 μg/m³ to be named as such. As touched on before, concentrations as high as this can cause many surface level respiratory issues, as well as many other more serious ones if exposure is particularly severe or happens over prolonged periods of time.

These more serious health issues will be covered in greater detail in short. With this data in mind, it is apparent that Washington, D.C., has sporadic events of pollution, and as such individuals should take preventative measures in order to ensure that their exposure to higher levels of PM2.5 are limited, particularly amongst vulnerable demographics. The use of air quality maps available on this page can help one determine whether any given day is experiencing a higher level of pollution or not, and for those on the go, the AirVisual app can also provide up to date readings on current air quality levels.

In closing, whilst Washington, D.C., has several spikes in its PM2.5 readings that place it in both the ‘good’ air pollution bracket (10 to 12 μg/m³ required) as well as the ‘moderate’ one, a majority of its readings taken over the month of March place it within the WHO's target goal, indicating that many of its days have respectable levels of air quality.

What are some health effects from breathing polluted air in Washington, D.C.?

As mentioned previously, there are a number of unpleasant respiratory issues that can occur when one inhales excessive amounts of ozone as well as the many other chemical compounds or hazardous particulate matter in the air. To delve into further detail regarding what can happen to an individual’s health when excessive pollution exposure occurs, there are a whole host of negative health effects that can arise amongst the population.

These include ones such as greater risks of cancer, particularly that of the skin, as well as the lungs. Due to the insidiously small size of PM2.5 (going down to sizes as small as 0.001 microns on beyond on occasion, as well as being comprised of many different carcinogenic and toxic materials), it can penetrate its way deeply into the lung tissue and from there enter into the bloodstream via the blood barrier, crossing over via the alveoli, or tiny air sacs that typically are used for the transferring of oxygen into the blood.

Once in the bloodstream, PM2.5 can wreak havoc on the bodies various functions, affecting the nervous system, causing damage to the blood vessels, as well as also disrupting various organs such as the liver, kidneys and even reproductive health, causing possibly reduced fertility rates. Cases of ischemic heart disease may present themselves, whereby the heart fails to receive adequate oxygen to its tissues and suffers from damage as a result. This can lead to a whole host of other issues, as well as other cardiac events such as increased risk of heart attack, arrythmias, and other serious conditions such as strokes occurring.

What are some other pollutants found in the air in Washington, D.C.?

Whilst many of the main pollutants have been discussed or mentioned earlier in the article, there would still be a variety of different pollutants permeating the atmosphere, being caused by many different sources that society as a whole typically doesn’t associate as being large producers of pollution. These sources include ones such as construction sites, road repairs, demolition areas as well as even certain household products contributing to the number of unwanted chemicals in the air (with these household products raising the indoor pollution levels across many homes).

One particularly salient pollutant is black carbon or soot as it is mainly known, with black carbon making up the majority of what ‘soot’ is. It is formed, along with VOCs, from the incomplete combustion of fossil fuels as well as the burning of organic matter, and as such it can find its creation in a huge variety of sources, ranging from indoor wood-burning appliances to vehicle engines and factory boilers (or anywhere that sees some form of combustion taking place).

Black carbon is part of the PM2.5 collective, and presents prominent health risks as a result, being highly carcinogenic, as well as having climate-changing properties. It can absorb solar radiation and convert it directly into heat, causing warming effects in areas where it has accumulated in larger amounts. It is typically found coated on roadside areas that see a large number of cars or vehicles passing through them, being both visually unappealing as well as causing damage to buildings, vegetation and wildlife.

As mentioned before, both nitrogen and sulfur dioxide (NO₂ and SO₂) are also on the main pollutant spectrum, and both find a majority of their release from vehicle engines, with NO2 being the biggest offender here. Both can also cause similar damage to the respiratory tract that ozone can, causing inflammation of the lung tissue as well as overall irritation to the mucous membranes and skin.

They can also both contribute to instances of acid rain, with the sulfur in SO2 adding greatly to this problem. In closing, some examples of the aforementioned VOCs include chemicals such as benzene, toluene, xylene and methylene chloride, all of which are highly dangerous, carcinogenic, as well as being able to maintain a gaseous state at much lower temperatures due to their volatile nature, hence easier to respire.

+ Article Resources
[1] American Lung Association. (2019). State of the air – 2019.
[2] Monitoring and Assessment Branch Air Quality Division Department of Energy and Environment. (2020). Ambient air quality trends report, 1996-2019.
[3] World Health Organization. (2020). Air quality guidelines – global update 2005.
[4] Goffman E. (2020, June 29). DC has cleaner air now. But as reopening plans continue, how can it keep the pollution at bay?