Air quality in Boston

Does Boston have clean air?

Boston air quality is generally considered clean for meeting all US Environmental Protection Agency (EPA) targets for criteria pollutants: PM2.5, PM10, ozone, carbon monoxide (CO), nitrogen dioxide (NO₂), and sulphur dioxide (SO₂). But despite the city’s success in achieving reduced pollution levels, Boston residents still breathe unhealthy air pollution during an average of 1.3 days a year.¹ The World Health Organization (WHO) warns that no level of pollution exposure has been shown to be free of health impacts.²

Of the criteria pollutants monitored and reported by the EPA in real-time, PM2.5 and ozone tend to be the most prevalent in US cities at dangerous levels. Boston PM2.5 and ozone pollution are similarly of primary concern.

PM2.5 describes airborne particles, such as soot, dust, dirt, metals, and chemicals, measuring 2.5 micrometers or less. Due to the very small size of PM2.5, these pollutants can become absorbed into the bloodstream when inhaled, causing far-reaching health effects. Exposure to PM2.5 has been associated with cardiovascular and respiratory disease, cancer, and early death.

For more than a decade, Boston air quality has met federal PM2.5 standards for annual and daily exposure. Current EPA standards, however, may still contribute to unnecessary deaths and adverse health effects. A study published by the Imperial School of Public Health concluded that further lowering the PM2.5 standard below the current level could provide an opportunity to save more lives and equalize the health of residents across income levels (as under-resourced communities often bear a disproportionate amount of pollution).³

The WHO employs a more stringent target, recommending annual PM2.5 exposure not exceed 10 μg/m³ (compared to the US standard of less than 12 μg/m³). By this standard, Boston’s 2018 PM2.5 concentration of 10.1 μg/m³ was unhealthy.

Of 24 monitored cities in Massachusetts, Boston’s PM2.5 levels rank as the 11th worst in the state out of 24 included cities. Townsend air quality, Amesbury air quality, and Natick air quality rank as the worst in the state, with PM2.5 levels of 10 μg/m³, 8.7 μg/m³, and 8 μg/m³ (respectively).

Ozone is a highly corrosive gas pollutant and key component of smog. When even small amounts of ozone react with the lungs, health effects can range from coughing and irritation to lung damage, cancer, and early death.

While Boston ozone pollution also passes federal guidelines, it is the primary cause for the average 1.3 unhealthy pollution days Boston experiences every year. As a result of these unhealthy ozone days, the American Lung Association (ALA) rated Boston a “C” grade for ozone, highlighting room for further improvement. Out of 229 metropolitan areas included in the ALA’s annual State Of The Air report, the Boston-Worcester-Providence area ranked 38th for high ozone days nationally.

How polluted is the air near my house in Boston?

While Boston averages healthy air quality overall, individual pollution exposure can vary greatly by neighborhood and proximity to major emission sources.

Residents who live near major pollution sources, such as new construction, major roadways, transportation hubs, and industrial complexes like factories, refineries, power plants, or other fossil-fuel burning complexes, are more likely to experience higher pollution levels.

Use the Boston air quality map or follow individual monitoring stations near you to better understand your own pollution exposure and risk.

What causes air pollution in Boston?

Boston air pollution comes from a combination of emission sources related to commercial, residential, and transportation activities.

Commercial sources, including various types of industry and large residential complexes, make up the largest emission source, accounting for 51.6 percent of Boston air pollution.⁴

Transportation comprises the next largest emission source, contributing to 28.6 percent of Boston’s air pollution mix. Most US cities have a larger share of pollution attributed to this source, often around 50 percent. Boston’s relatively low transportation share owes to the city’s density and strong public transportation system. More than half of residents commute to work using a mode of transportation other than a car.

Personal household emissions, including residential heating, wood burning, and barbecues. account for 19 percent of Boston’s air pollution mix, while wastewater treatment comprises the remaining 0.8 percent.

How does Boston keep air healthy?

Boston’s air pollution levels for PM2.5 and ozone have seen drastic improvements since 2003. Since then, the number of unhealthy pollution days has dropped from 26.1 to 1.3. Some of the largest reductions have been noted in the city’s stationary sources, including commercial, industrial, and large residential emissions.

Boston’s reduced emissions come despite a growing population and job market. Since 2005, Boston has grown from 520,000 to 680,000 residents. For the same period, Boston’s Gross City Product (GCP), a measure of economic growth, increased from 91 billion to 129 billion dollars. Boston’s emissions, meanwhile, fell 40 percent from 15.0 to 9.0 metric tons per year.

Boston’s success is attributed to a combination of local, state, and federal regulations that have gradually implemented more stringent limits and regulations on a wide variety of industry, transport, and personal activities.

Boston, meanwhile, benefits from its coastal location, city density, and robust public transportation system, which all further contribute to the city's clean air.

What are the most polluted places in Boston?

In Boston and cities across the country, under-resourced communities tend to bear a disproportionate level of air pollution. This correlation is the direct result of industrial zoning and disruptive city features that lower neighborhood values. Airports, major roadways, and industrial complexes are some examples of high-emission sources which tend to be intentionally located near lower-income communities.

In Suffolk County, Chelsea represents one such area that carries a heavier pollution burden than downtown Boston.⁵ Located at the cross hairs of the Tobin Bridge, Logan Airport, and various industrial centers, Chelsea has long been described by environmentalists as a troubling “sacrifice zone for the region” and as a community needing environmental justice

Demolition work on the Tobin Bridge during the middle of 2020 further coated much of the area in dust and emissions, with direct elevations noted in PM2.5 levels.

A large share of non-white groups live in these neighborhoods, and research has shown that these groups are more affected by poor air quality, often experiencing a higher prevalence of heart and lung disease as a result.

Follow real-time air quality levels in Boston at the top of the page. Due to the dynamic and fast-changing nature of air pollution, there is no substitute for real-time and forecast data.

+ Article Resources

[1] American Lung Association. (2020). State of the air – 2020.
[2] World Health Organization. (2020). Air quality guidelines – global update 2005.
[3] Bennett J, et al. (2019). Particulate matter air pollution and national and county life expectancy loss in the USA: A spatiotemporal analysis. DOI: 10.1371/journal.pmed.1002856
[4] City of Boston. (2017). Greenhouse gas emissions inventory 2005 - 2017.
[5] DeCosta-Klipa N. (2020, August 7). The EPA is taking a ‘first step’ toward addressing Chelsea’s air quality problems. Boston.