Qualité de l’air à Charlotte

Why does Charlotte have unhealthy air quality?

Charlotte’s unhealthy air quality owes to a combination of PM2.5 and ozone pollution. In 2019, Charlotte exceeded federal attainment standards for both pollutants. While its failure to meet ozone standards is consistent with recent years, its failure to meet annual PM2.5 targets was unusual. With exception of 2019, Charlotte has been within federal attainment levels for PM2.5 since 2010.

Charlotte air quality faces challenges inherent with a growing population and economy. Between 2004 and 2014, the Charlotte metro area was ranked as the fastest growing in the nation.¹ The city’s population, estimated most recently at about 886,000 residents, makes Charlotte the 15^th most populous city in the US.

With a growing population has come new construction as new residential units and office buildings rise to meet demand. Twenty skyscrapers are currently under construction, recently completed, or planned. New inroads and demand have contributed to Charlotte’s growth as a trucking and freight transportation hub for the East Coast. While these changes bring increased emissions and present challenges to maintaining downward trending pollution levels, long-standing emission sources in Charlotte comprise the largest portion of city-wide pollution.

Air pollution sources are often grouped into one of three sources: mobile sources (motor vehicles, trains and planes), stationary sources (power plants, petroleum refineries and factories), and area sources (agricultural areas and wood burning fireplaces).

In metropolitan US cities, mobile sources, including emissions from cars and trucks, tend to comprise more than half of a city's pollution emissions.² Cutting emissions here by moving towards cleaner fuel and more fuel-efficient, low-emission vehicles, such as electric or hybrid vehicles, often represents one of the greatest opportunities for cities to reduce their pollution levels.

Stationary emission sources in Charlotte make up the next largest share of emissions and account for 38 tons of PM2.5, 323 tons of PM10, 1,131 tons of VOCs, and 388 tons of NO₂.³

Does Charlotte meet EPA air pollution standards?

Charlotte failed in 2019 to meet Environmental Protection Agency (EPA) standards for the nation’s two most prevalent and harmful air pollutants: ozone (O3) and fine particulate matter (PM2.5), in 2019.

Ozone (O₃) is a highly corrosive gas pollutant that attacks the lungs by reacting chemically with them. Unlike most pollutants measured and managed by the EPA, ozone is a secondary pollutant, meaning that it is generally not released directly but rather created in the atmosphere when primary pollutants react in sunlight. Breathing ozone can cause chest pain, coughing, shortness of breath, and throat irritation. Long-term damage can include permanent lung damage, asthma, and chronic obstructive pulmonary disease (COPD).

Federal ozone standards are stated in terms of an allowance of unhealthy ozone days. Cities that exceed a two-year weighted average of 3.2 unhealthy pollution days fail to meet EPA guidelines. From 2016 to 2018, the most recent monitoring period evaluated in the American Lung Association “State of the Air” report, Charlotte air quality recorded an average 4.7 unhealthy ozone days, exceeding the target by roughly 47 percent.⁴ This weighted average attempts to account for days that are “orange” (unhealthy to sensitive individuals), “red” (unhealthy to general public), and “purple” (very unhealthy) as a ratio of their risk level. In 2018, Charlotte experienced 14 “orange” days, but no days in the “red” or “purple” category.

PM2.5 pollution is the mix of suspended particulate matter measuring less than 2.5 micrometers. Its small size, rather than its chemical makeup, gives this pollutant its defining characteristic of being able to penetrate deep into the lungs, sometimes bypassing the blood barrier and causing far-reaching health implications.

The US EPA advises that annual PM2.5 concentrations not exceed 12 μg/m³, or the US AQI “good” threshold. The World Health Organization (WHO) uses a more stringent guideline, targeting annual PM2.5 levels no more than 10 μg/m³. In 2019, Charlotte exceeded both pollutant targets for the first time since 2013 with an annual average of 12.2 μg/m³.

Seven months in 2019 averaged PM2.5 ratings in the “moderate” US AQI category: May (12.7 μg/m³), June (13.9 μg/m³), July (15.6 μg/m³), August (15 μg/m³), September (16.3 μg/m³), November (13.7 μg/m³), and December (12.2 μg/m³). While monthly averages are not a measure regulated by the EPA, Charlotte’s high PM2.5 levels here gave way to its high annual levels.

Follow Charlotte live air quality data at the top of this page. Colors match corresponding EPA levels, while the mentioned “main pollutant” marks which pollutant, generally PM2.5 or ozone, is at the most risky concentration, causing the pollution color (yellow, orange, red).

Where does Charlotte smog come from?

Smog describes reduced visibility as a result of air pollutants. High ozone and particle pollution (PM2.5 and PM10) levels are most often attributable to smoggy conditions. Charlotte smog is the result of a pervasiveness of both of these air pollutants, which tend to be present at exceedingly high levels in the summer and winter.

Charlotte’s climate is described as humid subtropical. More than 130 days a year are above 80°F.⁵ The prevalence of warm days increases the likelihood for ozone formation, which requires sunlight, precursor pollutants (nitrogen dioxide and volatile organic compounds), and temperatures above 84°F to form. As a result of high temperatures required for ozone formation, Charlotte’s ozone season runs from May to September. During these months, Charlotte air quality experienced 14 “orange” days for unhealthy ozone in 2018. Ozone alerts are especially common in the afternoon when direct sunlight and temperatures are at their strongest.

While summer PM2.5 levels in Charlotte are typically relatively low, August and September were Charlotte’s most PM2.5 polluted months in 2019. The combination of high PM2.5 and ozone levels led to particularly smoggy conditions that season.

Charlotte winter smog, on the other hand, tends to be a result of increased PM2.5 levels as a result of wood burning, home heating, and car idling as well as a weather event described as a “cool air inversion.” Cool air inversions occur when cold ground-level air, often as a result of snow coverage or ice, becomes trapped under warmer denser air above. The polluted surface air, unable to disperse into the atmosphere normally, creates a brown cloud which hangs over the city.

Transboundary smog stemming from nearby cities is another source of Charlotte’s air pollution. Albemarle air quality is the worst in North Carolina, with an annual PM2.5 concentration of 14.6 μg/m³. Albemarle is less than 40 miles from Charlotte.

What are the health effects of Charlotte air pollution?

The US Environmental Protection Agency (EPA) relates concentration levels of six criteria pollutants to health threat by using an Air Quality Index (AQI) scale. The AQI helps to convey the level of risk in the air when the air contains more than one pollutant.

The EPA targets “good” air quality for all cities (color code “green”). Levels in excess of this may be classified as either moderate (yellow), unhealthy for sensitive groups (orange), unhealthy (red), very unhealthy (purple) or hazardous (maroon), respectively.

While “moderate” pollution levels exceed federal targets, “unhealthy” action days only refer to periods when pollution levels are defined as “orange” (unhealthy for sensitive groups), or higher. Charlotte air quality experienced 14 days of “orange” air pollution in 2018, which placed sensitive groups at risk for expriencing adverse health effects.

Sensitive groups include individuals with pre-existing heart and lung conditions, children, and the elderly, who are more likely to experience acute health effects. In Mecklenburg County, of which Charlotte is the county seat, there are 109,194 individuals with asthma, 61,333 with COPD, 728 with lung cancer, 71,907 heart disease, 257,713 children under 18, and 122,549 adults over 65.

Adverse health effects also tend to disproportionately affect individuals with fewer economic resources and political power. Residents of the Historic West End neighborhood, for example, are surrounded by industrial zoning, highway construction, waste sites, truck stops, factories, and other large emitters.⁶ The high concentration of air pollution sources here increases these resident’s risk of heart disease, stroke, and asthma, three of the leading causes of death in North Carolina. Not only do these underserved communities tend to experience higher levels of pollution, their homes also often lack robust air filtration and insulation to keep their indoor spaces safe. As a result of bearing much of Charlotte's pollution burden, the Historic West End community experiences worse health outcomes than those in the Dilworth / Myers Park communities.

The inequitable environmental effects experienced by these residents is no fault of their own but rather a result of commercial and government operations: an environmental justice issue that must be addressed. Clean Air Carolina (CAC) is one such group that is striving to meet this imbalance and serve the communities here by providing needed air quality monitoring and educational resources. Dozens of CAC’s independently operated air quality monitors in North Carolina can be viewed on their IQAir contributor page.

Follow Charlotte live air quality data and health advisories to guide precautionary actions to reduce your health risk.

Is Charlotte air quality getting better?

Charlotte air quality has improved dramatically over recent decades. Measures for overall air quality (AQI), PM2.5, and ozone pollution, have all seen significant gains.

The air quality index (AQI) provides a summary of air quality by conveying the level of health risk in the air using the pollutant at the most dangerous level. Since 2004, the number of days averaging a “good” AQI has more than doubled from slightly more than 100 to more than 230 days.⁷ Only 3.8 percent of days, moreover, are categorized as unhealthy for sensitive groups, down from roughly 6.5 percent in 2004.

Charlotte ozone levels have similarly seen significant improvements. The worst ozone levels were recorded in the 1997 to 1999 monitoring period. During that time, Mecklenburg County experienced an annual weighted average of 92.2 unhealthy ozone days.⁸ From 2016 to 2018, however, that number was reduced to 4.7 unhealthy days, close to the federal target of 3.2 days.

Improvements in Charlotte’s air pollution levels are owed to increasingly strict state and federal regulations on industrial facilities and motor vehicles. These regulations include:

• 1990 Amendments to the Clean Air Act enforced limits on large source emitters and implemented more rigorous monitoring
• The 2002 Clean Smokestacks Act set emission limits on North Carolina’s coal-fired power plants to reduce the prevalence of ozone precursors and particle-forming emissions
• More stringent federal standards for motor vehicles, petroleum, and diesel fuel
• Local grants to replace aging diesel engines, implement cleaner energy, and promote electric vehicles

+Article Resources

[1] U.S. Census Bureau, Population Division. (2019). Annual estimates of the resident population: April 1, 2010 to July 1, 2018.
[2] National Park Service. (2020). Where does air pollution come from?
[3] Mecklenburg County Air Quality. (2013). Stationary sources.
[4] American Lung Association. (2020). State of the air – 2020.
[5] Current Results. (2020). Charlotte temperatures: averages by month.
[6] Cupini C. (2020, April 22). Clearing the air in the Historic West End.
[7] Mecklenburg County Air Quality. (2020). Mecklenburg County air quality is improving.
[8] American Lung Association. (2018). New air quality report finds North Carolina’s ozone pollution worsened, year-round particle pollution improved.