Report on Air Quality Trends in the District of Columbia

The District of Columbia has greatly improved its air quality over the recent decades.

In the 1960s, the District established one of the nation's first ambient air monitoring stations. Today, the District’s ambient air monitoring network consists of six stations: McMillan Reservoir, River Terrace, Takoma Recreation Center, King Greenleaf Recreation Center, the Anacostia Freeway Near-road Monitor, and Bald Eagle Recreation Center. Hains Point was temporarily closed in 2016 for building renovations and permanently in 2017 due to site inaccessibility. The Verizon Center monitor was shut down at the end of December 2016. King Greenleaf Recreation Center officially became part of the ambient air monitoring network in January 2018. In March 2024, DOEE added its sixth station at Bald Eagle Recreation Center, located in an overburdened environmental justice (EJ) community in Ward 8. This EJ station is funded by the federal American Rescue Plan (ARP) Direct Award Air Monitoring grant.

Pollutants are emitted by sources referred to as "stationary sources" and "mobile sources." Stationary sources have a fixed location and can emit a variety of pollutants depending on the purpose of the source. Mobile sources do not have a fixed location and are generally propelled or operated using an internal combustion engine.

Large stationary point sources are individual facilities with smokestacks, such as factories or power plants. They are also classified as electric generating units (EGUs) or non-EGUs. Non-EGUs include facilities such as universities, large hotels, and hospitals. Some inventories consider rail yards and airports as non-EGUs.

Smaller stationary sources, termed nonpoint, are not identified individually because they have more of an impact collectively. Some examples include small industrial or commercial facilities, home heating and cooking, gas stations, printing operations, and auto maintenance facilities.

Mobile onroad vehicles are any moving vehicles that are permitted to travel on highways and include cars, trucks, buses, and motorcycles.

Mobile sources that are not used on roads are termed "nonroad mobile." This sector includes forklifts, construction equipment, and lawn mowers. Some inventories consider rail lines and marine vessels as nonroad though some separate them out.

The Clean Air Act (CAA) requires the establishment and operation of air monitoring networks to measure ambient air quality. The Environmental Protection Agency (EPA) then compares the data from the different networks to the health based National Ambient Air Quality Standard (NAAQS) for the pollutant. The air pollutants that have a NAAQS set by EPA are called "criteria pollutants." When criteria pollutants exceed the standards, state and local agencies such as DOEE engage in an air quality improvement process. The steps in this improvement process include:

• Planning and Regulatory Development: Under the CAA, areas in nonattainment of the NAAQS for a particular pollutant are required to develop long-term plans (called “state implementation plans” or SIPs) to meet the NAAQS. SIP strategies to control emissions from specific types of sources must be quantifiable, surplus, permanent, and enforceable. The District develops both mandatory regulations and voluntary policies, often in collaboration with neighboring states, to maintain existing air quality and further reduce emissions. These plans must be approved by EPA and once in effect are enforceable by both the District and EPA.
• Permitting: The largest sources of pollution are required by law to acquire permits that allow them to pollute based on a mutual agreement that specified conditions will be met. Emissions limits in permits can initiate the installation of control technologies or necessitate operational or work practice changes. Noncompliance with final permits is enforceable.
• Enforcement and Compliance: DOEE ensures that the regulated community complies with applicable permits and other legal and regulatory requirements by inspecting facilities, reviewing reports, and issuing fines for noncompliance.
• Monitoring and Assessment: Ambient air quality monitoring is the “litmus test” that reveals the effectiveness of the air quality program. Monitoring results are compared with air quality projections to influence decision-making.

The EPA set national ambient air quality standards (NAAQS) for six common pollutants: ground-level ozone, lead, carbon monoxide, fine and coarse particulate matter (PM _2.5  and PM ₁₀ ), nitrogen dioxide, and sulfur dioxide. These pollutants threaten human health and public welfare. When ambient air quality in the jurisdiction exceeds the NAAQS for a criteria pollutant, the area is said to be in "nonattainment" for that pollutant.

The World Health Organization (WHO) provides a set of guidelines that are evidence-based recommendations of limit values for specific pollutants. These limit values, or Air Quality Guidelines (AQG), serve as a guidance for countries to protect public health. The pollutants of concern include fine and coarse particulate matter (PM _2.5  and PM ₁₀ ), ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide.

Here, we present an analysis on ambient air quality trends in the District. This trends report demonstrates that despite population, employment, and housing increases, ambient concentrations of all criteria pollutants have dropped since the late 1990s. Improvements in air quality are likely attributed to several air pollution reduction regulations. However, there is still work to be done to protect human health and welfare in the District.

Emission analysis is also presented in this trends report. Air pollution emission sources are broken up into four sectors between point sources, nonpoint or area sources, nonroad, and onroad sources. These emissions are reported to EPA every three years to be included in the National Emissions Inventory (NEI), which is a national database of emissions provided by state, local, and tribal air agencies from their jurisdiction combined with supplemental national default data estimates provided by EPA. The latest NEI available for public view is from 2017. These emission inventories are used to evaluate air quality and effects of regulations passed. Emissions of pollutants can be minimized using technology at a source or by adapting how or when a source is used.

Ground-level ozone is one of the most common air pollutants. Ozone is a gas made up of three oxygen atoms. It occurs naturally high above the Earth in the stratosphere (about 31,000 to 164,000 feet above the ground), where it helps protect us from the Sun’s harmful ultraviolet rays. However, ozone near the ground, in the troposphere (up to about 31,000 feet above the ground), is harmful to our health. Too much ground-level ozone can cause breathing problems, trigger asthma attacks, and reduce lung function. This type of ozone isn’t released directly into the air. Instead, it forms when pollutants from cars, factories, and other sources—called volatile organic compounds (VOCs) and nitrogen oxides (NOₓ)—react with sunlight and heat. That’s why ozone pollution is more common during hot summer months in the District.

Ground-level ozone is currently measured at three monitoring sites in the District: McMillan, River Terrace, and Takoma Recreation Center. The National Ambient Air Quality Standards (NAAQS) are federal air quality limits set by the EPA to protect public health and the environment. For ozone, the 2015 NAAQS limit is 70 parts per billion (ppb) over an 8-hour period. Data is collected hourly, and 8-hour rolling averages are calculated for every hour of the day. The fourth-highest 8-hour average for the year is identified, and the "design value" is calculated by averaging the fourth-highest readings from three consecutive years. The year of the design value refers to the last year in that three-year period.

The World Health Organization (WHO), an international public health agency, has more stringent ozone recommendations than the EPA’s National Ambient Air Quality Standards (NAAQS). WHO’s guideline levels, called Air Quality Guidelines (AQG), are designed to protect public health by setting safe limits for air pollutants. For ozone during the peak season, WHO recommends an AQG level of 60 μg/m³ (approximately 35 ppb). This value is based on the average of daily maximum 8-hour ozone concentrations over the six consecutive months with the highest running averages. WHO also provides a short-term recommendation of 100 μg/m³ (approximately 50 ppb), based on the 99th percentile of daily maximum 8-hour ozone concentrations in a year.

Particulate matter (PM) is the mixture of airborne solid particles and liquid droplets at various sizes. PM can range from extremely small particles (smoke and soot) to larger sized dusts and industrialized particles. Some particles are formed by complex reactions of gaseous pollutants in the atmosphere, so called secondary particulate matter. Precursors for fine inhalable PM include ammonia, SO ₂ , and NO _x . Sulfates, nitrates, organic carbon, and elemental carbon contribute to the make-up of condensable fine PM.

Particulate matter is classified into three different sizes: PM ₁ , PM _2.5 , and PM ₁₀ . PM _2.5 , or fine particles, is defined as particles with diameters that are generally 2.5 micrometers or less. PM ₁₀ , or coarse particles, are inhalable particles that are generally 10 micrometers and smaller. PM ₁ , or ultra fine particles, are defined as particles with diameters that are generally 1 micrometers or less, though PM ₁  has not yet been evaluated by EPA for a separate NAAQS.

The District measures PM _2.5  at four locations: Near-road, River Terrace, McMillan, and King Greenleaf. PM ₁₀  is currently only measured at McMillan. The annual PM _2.5  NAAQS is measured using the arithmetic mean of four quarterly averages per year. The 24-hour standard is based on the 98th percentile reading per year, where data is ranked from highest to lowest. Over the last two decades, the District has seen a drop in annual and 24-hour PM _2.5  levels. The design value for PM ₁₀  is calculated by taking the second highest daily mean max concentration in a calendar year averaged over three consecutive years.

WHO provided recommendations of AQG levels for both PM _2.5  and PM ₁₀  at different averaging times (annual and 24-hour). The recommended PM _2.5  AQG level with an annual averaging time is 5 μg/m ³  while the 24-hour AQG level is 15 μg/m ³ . On the other hand, the recommended PM ¹⁰  AQG level with an annual averaging time is 15 μg/m ³  while the 24-hour AQG level is 45 μg/m ³ . These guidelines are stricter than the current EPA NAAQS.

In 1997, the Environmental Protection Agency (EPA) established National Ambient Air Quality Standards (NAAQS) for Fine Particulate Matter (PM2.5), leading to the creation of the PM2.5 Chemical Speciation Network (CSN) in 2000. This network is a component of the National PM2.5 Monitoring Network. The primary goal of the National PM2.5 Monitoring Network is to determine if areas meet the NAAQS for PM2.5. CSN data is not used for regulatory decisions, meaning, it is not used to determine whether or not an area is in attainment with the PM2.5 NAAQS, but they do play a crucial role in evaluating long-term air quality trends and quantifying the impact of specific sources on particulate matter concentrations, especially PM2.5. In this case, chemical speciation refers to the collection of all the metals, compounds, and other materials that make up particulate matter.

PM2.5 monitoring typically occurs in urban areas, such as the District of Columbia, and provides valuable insights into the chemical composition of PM2.5 and its effects on human health. Since January 1, 2002, the District of Columbia has been conducting PM2.5 Chemical Speciation monitoring, with samples collected every three or six days, depending on the instrument. These samples are then sent to a lab for analysis, giving us a comprehensive dataset to study the components of PM2.5 that can negatively affect residents in, and visitors to, the District of Columbia.

Below are three instruments used by the Department of Energy and Environment's air quality monitoring team to measure particulate matter (PM) and its components. These measurements are collected at our McMillan Reservoir site.

From sample collection to viewing the final data on a computer screen, the process of analyzing air quality is intricate and involves multiple steps. Here is a flow diagram that outlines this process, providing a comprehensive overview of the journey from raw samples to meaningful data.

PM2.5 refers to fine particulate matter with a diameter of 2.5 micrometers or smaller. This type of air pollution is particularly concerning because the tiny particles can penetrate deep into the respiratory system, reaching the lungs and even entering the bloodstream. The chemical speciation of PM2.5 involves identifying and characterizing the various chemical components that make up these fine particles. Understanding the chemical composition is helpful for identifying the source of the particulate matter. Here are some of the most common components of PM2.5.

• Sulfates (SO4): Derived from sulfur dioxide emissions, often from power plants or industrial sources. Roughly 99% of the sulfur dioxide in the atmosphere comes from human activity. Sulfur oxides combine with other molecules to form particles that contribute to particulate pollution, creating hazy skies with reduced visibility.
• Nitrates (NO3): Nitrates are compounds containing the nitrate ion (𝑁𝑂3−NO3−​). They are used in various industrial processes, including fertilizer production and explosives. In the context of air pollution, nitrates can form from nitrogen oxides (NOx), which are emitted by vehicles, power plants, and industrial facilities. Once in the atmosphere, nitrates can contribute to the formation of fine particulate matter (PM2.5), a key component of smog.
• Ammonium (NH4): Ammonia is a compound of nitrogen and hydrogen, resulting from agricultural and industrial processes. Gaseous ammonia reacts with other pollutants in the air to form fine particles of ammonium salts, which affect our ability to breath. The image below is from a study conducted by Harvard University researchers, Fabien Paulot and Daniel Jacob, using a NASA model of chemical reactions in the atmosphere to better represent how ammonia interacts in the atmosphere to form harmful particulate matter. The map shows an increase in the annual mean surface concentration of particulate matter resulting from ammonia emissions associated with food export. Populated states in the Northeast and Great Lakes region, where particulate matter formation is promoted by upwind ammonia sources, carry most of the cost.

• Organic Carbon (OC): Organic carbon in particulate matter (PM) refers to carbon-based compounds found within airborne particles. Examples of these carbon-based compounds include Hydrocarbons like coal or petroleum and Polycyclic Aromatic Hydrocarbons (PAHs) like benzene. Organic carbon sources include vehicle emissions, biomass burning (think forest fires, agricultural burning, and residential wood burning) as well as industrial emissions.
• Elemental Carbon (EC): Also known as black carbon, is carbon in its pure form. It is known for its black color and light-absorbing properties. Elemental carbon plays a significant role in climate change due to its ability to absorb sunlight, contributing to urban heat islands. Major sources of elemental carbon are emissions from vehicle exhaust, especially from diesel engines, industrial processes, and biomass burning.

Many of the components of PM2.5 contribute to the formation of haze. Haze occurs when fine particles are suspended in the air, causing reduced visibility. This reduction in visibility is due to light scattering, which happens when light waves interact with the suspended particles. The scattered light creates a white or grayish appearance in the atmosphere. In addition to the negative aesthetic effects, haze makes it very hard for drivers and pilots to navigate.

Haze can greatly reduce visibility, as shown in the image below. The image was taken at Shenandoah National Park and depicts a good visibility day (no haze) and a bad visibility day (a day with no haze). The visual range is greatly reduced on hazy days. The District, like every jurisdiction, must also eliminate its contribution to haze in national parks, like Shenandoah National Park, through its work with the Mid-Atlantic Northeastern Visibility Union (MANE VU). For more information, check out this website:  About MANEVU - MANEVU (otcair.org) 

Diesel engines are a significant source of particulate matter (PM) in the District, contributing substantially to air pollution. These six elements are of particular concern due to their toxicity and prevalence in diesel emissions, making them essential subjects for study and monitoring efforts. Below is a graph illustrating the levels of particularly harmful components of particulate matter in the District over the years.

The EPA’s Health Effects Notebook for Hazardous Air Pollutants provides detailed fact sheets about various pollutants and appropriate levels of exposure ^[1] . These fact sheets include minimal risk level (MRL) evaluations provided by the Agency for Toxic Substances and Disease Registry (ATSDR). The MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse noncancer health effects over a specified duration of exposure.

Fact sheets are available for arsenic, cadmium, lead, and nickel, and the concentrations of these four pollutants in the District fall below the thresholds determined by the ATSDR. . While not mentioned in the EPA fact sheets, the EPA conducted a study where they found the average concentration of copper across 15 US sites ranged from 0.013 to 0.0792 µg/m³  ^[2] . The District's concentrations are well below this range.  Additionally, according to the MRL fact sheet provided by the ATSDR for vanadium, the District's levels are below both the acute threshold of 0.0008 mg/m³ and the chronic threshold of 0.0001 mg/m³  ^[4] .

Understanding their presence in diesel emissions and monitoring their levels is crucial for mitigating air pollution and safeguarding public health. To learn more about the impacts of diesel fuel emissions, check this link out:  Learn About Impacts of Diesel Exhaust and the Diesel Emissions Reduction Act (DERA) | US EPA 

In June 2023, the District of Columbia experienced a significant decline in air quality due to wildfire smoke from different locations in the Continental US. This resulted in some of the worst air quality conditions observed for the month of June in recent years.

While wildfire season in Canada typically varies depending on the region and prevailing weather conditions, most wildfires occur between April and September. In 2023, Canada was affected by a record-setting series of wildfires, beginning in March, and with increased intensity starting in June. Over the course of last year’s fire season, it is estimated that roughly 18.4 million hectares (~71,042.8 sq miles), about the size of North Dakota, were burned.  [i] This is well above the 2.5 million hectare (9,652.5 sq miles) per year average in Canada.  All 13 provinces and territories were affected, most notably, Nova Scotia and Quebec.

Additionally, in June 2023, we also felt the effects of wildfires originating from a much closer area to the District: New Jersey, which is roughly 187 miles away. This year marked a significant wildfire season for our neighboring state. John Cecil, Assistant Commissioner for State Parks, Forest & Historic Sites, stated, “In 2023 we saw the busiest wildfire year in over 20 years with 14 major wildfires burning across New Jersey threatening over 200 homes, forcing evacuations and closing roads.” [ii] 

While these devastating fires posed significant challenges for residents of their respective state/province, their effects were also felt here in the District of Columbia. Carried by prevailing winds and high-altitude air currents, smoke from these wildfires traveled hundreds of miles, and blanketed our skies,

leading to poor air quality and heighted health risks for our residents. Smoke, which contains harmful particulate matter such as PM2.5, when inhaled can exacerbate respiratory conditions, trigger asthma attacks, and increase the risk of heart and lung diseases. This is especially harmful for vulnerable populations such as children, the elderly and individuals with preexisting conditions, that make them more susceptible to respiratory issues or other health complications heighted by poor air quality.

Below is a more detailed look at some of the fires that contributed to poor air quality in the District for the month of June 2023.

Nova Scotia experienced its largest recorded wildfire in its history with the Barrington Lake fire in Shelburne County, which is in the southwestern region. The fire, which broke out on May 26, 2023, was declared under control on June 13 and extinguished on July 26. The Barrington Lake fire was nearly 25,000 hectares (96.5 sq miles) and resulted in the evacuation of nearly 5,500 people. (see image below) Smoke from the Barrington Lake fire, reached the District as early as May 31 ^st  as depicted in satellite imagery, showing a heavy smoke plume entering our area around that day.

While wildfires devastated Nova Scotia, the District of Columbia also faced challenges from wildfire smoke originating from New Jersey. Between May 29 ^th  and June 2 ^nd , New Jersey experienced several significant fires, all contributing to the presence of smoke in the District during this period. These fires include the Box Turtle fire, burning 64 hectares (0.25 sq miles) on May 29 ^th , the Allen Road fire, consuming 896 hectares (3.46 sq miles) from May 31 ^st  to June 2 ^nd , the Fort Dix fire covering roughly 31 hectares (0.12 sq miles), and the Flat Iron fire on June 2 ^nd , with a burnt area of about 35 hectares (0.13 sq miles). Despite the varied locations and sizes, their combined impact contributed to poor air quality in the District during this timeframe.

Later in the month, around June 28 ^th  -29 ^th , we felt the effects of another wildfire, this time originating from Quebec. Despite the distance, Quebec being approximately 580 miles away from the District of Columbia. Interestingly enough, the wildfires started earlier in the month, beginning June 1 ^st  and ending June 25 ^th , culminating in the largest single fire recorded in southern Quebec, covering a total of 460,000 hectares (approximately 1,776 sq miles). The smoke from these wildfires was carried over such a great distance by the jet stream. Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere and typically blow from west to east. The smoke was able to rise high enough into the atmosphere, get caught in the jet stream, and was able to be transported to the District, reaching us in late June.

We witnessed PM2.5 concentrations reach unprecedented levels, particularly on June 8th. To understand the movement of air and the dispersion of pollutants, meteorologists rely on tools like NOAA HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory). This computer model tracks the movement of air. It is particularly valuable for tracking the dispersion of air pollutants, like smoke or airborne particles, throughout the atmosphere. In figure 1, we examine a backward trajectory, illustrating the source of the air. This trajectory, representing a 48-hour simulation starting from June 8, at 14 UTC (10:00 am EST) and ending on June 8, 2023, at 14 UTC (10:00 am EST), provides valuable insights. It reveals that air masses originating from Canada, the source of many of the June 2023 fires, have impacted our area. Different heights of the air are depicted in the trajectory: 4000 meters (green), 2500 meters (blue), and 500 meters (red) above ground level. At the 500-meter height, although originating in Canada, the air travels through New York, Pennsylvania, and New Jersey before arriving in the District. This is important because the wildfire smoke from New Jersey is contributing to the wildfire smoke from Canada, resulting in especially poor air quality for June 8th.

The figure below provides an illustration of PM2.5 concentrations at various monitoring sites throughout the District, not only during the month of June 2023 but compares this data to 20-year average concentrations. This allows us to see the extent to which the wildfire smoke influenced air quality in the region. Here, you can see the drastic peak on June 8th, indicating a significant impact from the wildfire smoke. Other notable peaks would be the June 1st peak, which aligns with the start of many of the New Jersey fires and the Nova Scotia wildfires, and the June 29th peak, which aligns with the Quebec wildfires.

For a more in-depth analysis of the wildfire events on June 1, 2, and 29 as they relate to ozone pollution, you can read the exceptional event analyses we submitted to EPA:  Air Quality Exceptional Events | doee (dc.gov) .

Nitrogen dioxide (NO ₂ ) is a brownish and highly chemically reactive gaseous pollutant. It is the indicator of a class of compounds called nitrogen oxides (NO _x ), which react in the atmosphere to form ground-level ozone and fine particulate pollution. NO ₂  is formed during high-temperature combustion of fuels and by vehicle engines and industrial processes, such as electricity generation. Studies have shown that long-term exposure to NO ₂  causes symptoms of bronchitis in asthmatic children.

NO ₂  is currently measured at four locations: River Terrace, McMillan, Takoma Rec, and the Near-road sites. The 2010 1-hour NO ₂  standard of 100 ppb is the 98th percentile of 1-hour daily maximum concentrations, averaged over three consecutive years. The annual NAAQS of 53 ppb is the average of hourly measurements per year.

WHO also set guidelines to protect the public from NO ₂ , that were far more stringent than the NAAQS. The long-term exposure AQD level was set to 10 μg/m ³  (≈5.3 ppb) for the annual mean and the 24-hour mean was set to 25 μg/m3 (≈13.3 ppb).

Sulfur dioxide (SO ₂ ) is a highly reactive gas that forms both from the burning of fuels containing sulfur (mainly coal and oil) and during industrial processes, such as metal smelting and oil refining. It can also be produced from the burning of diesel fuel in mobile sources. It is one of a group of oxides of sulfur. When combined with other pollutants and chemicals, SO ₂  can react with oxygen and water in the atmosphere to form acid rain. Short-term exposure to SO ₂  can make breathing difficult.

Historically, the District measured SO ₂  only at River Terrace. However, measurements of the criteria pollutant currently take place at the McMillan site. The River Terrace monitor was shut down due to building renovations of the site location from March 2014 to May 2016. Due to this, the station did not have a complete and valid SO ₂  design value until 2019. The design value is determined by the 99th percentile of 1-hour daily maximum concentrations, averaged over three consecutive years. The 1-hour NAAQS value is set for 75 ppb. The District has consistently remained below the NAAQS for nearly two decades.

WHO designated the 24-hour mean AQG level to be 40 μg/m ³  (≈15.3 ppb) for SO ₂ , which is lower than the EPA's NAAQS, but with a longer averaging time.

Carbon monoxide is a colorless, odorless gas that is poisonous at high concentrations. When it enters the bloodstream, it reduces the capacity of the body to deliver oxygen to organs and tissues. The highest concentrations tend to occur during the winter months due to the "cold starting" of automobile engines.

The District currently measures carbon monoxide at two sites: McMillan and Near-road. Concentration levels have remained well below the NAAQS value for the last two decades. For the 8-hour standards, hourly measurements are averaged over eight hours on a backward-rolling basis to establish the daily 8-hour averages. The second highest maximum reading is taken per year to determine an annual estimate, and the DV is the highest annual estimate over two consecutive years.

WHO recently established a new recommendation for carbon monoxide. The 24-hour AQG level was set to 4 mg/m ³  (≈3.5 ppm). Compared to the EPA's NAAQS, this value is lower, but the averaging time is longer. This recommendation was based on recent research of the effects of short-term concentrations on hospital admissions.

Lead is a metal found naturally in the environment and in manufactured products. The highest levels are usually found near lead smelters, where lead is extracted from ores. High exposure to lead can result in serious neurological damage. Historically, lead air pollution was more common when lead was included in gasoline, but that was completely phased out in 1996, though this lead air pollution has since deposited in the soil and remains with us to this day. Young children and infants are very sensitive to lead exposures. The rolling 3-month average lead NAAQS value is 0.15 μg/m ³ .

The District began operating population-based ambient lead monitors in January 2012 and collected data from 2012 through 2015. Concentrations of lead were consistently low and DOEE discontinued the lead monitor at the end of 2016 under the provisions of Title 40 of the Code of Federal Regulations (C.F.R.).

Volatile organic compounds (VOCs) are important pollutants to measure because they are involved in the photochemical reactions that form ground-level ozone. It is sometimes the case that individual VOCs, such as benzene, are also hazardous air pollutants (pollutants known to cause cancer or other serious long-term health problems). Some sources of VOCs include power plants, industrial processes, vehicle exhaust (onroad and nonroad), and commercially available products such as paints, insecticides, and cleaning solvents. VOCs also come from natural sources such as trees and other plants.

Since 2008, the nonpoint sector have produced the highest anthropogenic emissions of VOCs, followed by the onroad sector. Overall, the District has seen a downwards trend in VOC emissions since 1996.

Emissions are calculated using data about how much activity occurs in a sector, along with technical information about the emissions source (such as a typical emissions rate). Emissions measurements from a particular source or activity are not always possible; hence, air pollution emission estimates based on proven methods are typically used. Estimation methodologies can change over time as new information becomes available. EPA gathers and develops emissions data for the following criteria pollutants and their precursors: NO _x  and VOC (ozone precursors), CO, PM (primary, condensable, and filterable emissions data for both coarse and fine PM), and SO ₂  in short tons per year (tpy). Based on official EPA National Emissions Inventory (NEI) estimates (not including natural biogenic sources), emissions of criteria pollutants and their precursors in the District have dropped gradually since 1996 despite increases in population, employment, and households over time.

The interactive graph below depicts NEI emission values of several pollutants in the District for different years (2011, 2014, 2017). To evaluate sources of a specific pollutant, first select the NEI year, then the pollutant and lastly, the sector. To compare different pollutants, simply click on the names of the pollutants you wish to evaluate. The entire NEI dataset from the District is located on Open Data DC:  Emissions Inventory .

Climate change refers to the long-term shift in Earth's weather conditions. It is one of the most challenging problems of our time that requires global action. A major driver of climate change is an increase in the anthropogenic emissions of greenhouse gases. Greenhouse gases (GHGs) are pollutants that trap heat in the upper atmosphere and influence the global climate. The three major GHGs are carbon dioxide (CO ₂ ), methane (CH ₄ ) and nitrous oxide (N ₂ O). Since CO ₂  in particular is a by product of burning fossil-fuels, many of the solutions to reduce CO ₂  emissions can also lead to reductions in the harmful air pollutants such as NO _X , PM _2.5 , SO ₂ , and CO discussed earlier.

Since the Industrial Revolution, there’s been a steady increase in CO ₂  and other GHGs. The figure below illustrates the recorded CO ₂  levels at Mauna Loa Observatory since 1958. The red line indicates the mole fraction of CO ₂  in dry air and the black line indicates the seasonally corrected data.

This increase in CO ₂  has led to a rise in global temperatures. According to the World Meteorological Organization (WMO), years 2015 to 2021 are the seven warmest years on record. This heating of the atmosphere has contributed to more frequent and extreme weather events. Globally, warmer temperatures can directly and indirectly lead to more destructive hurricanes, flooding, forest fires, drought and higher sea levels. Locally, a rise in temperatures lead to an increasing frequency of warmer than average days and intense storms and flooding. As climate change continues to affect the global climate and increase temperatures, meeting ozone standards and ensuring healthy air within the District will become more challenging.

The District has remained committed to reducing its impact on the atmosphere and preparing for the changing climate. DOEE released the Sustainable DC 2.0 plan which established the District’s commitment to reduce GHG emissions by 50 percent below 2006 levels by 2032. The District is currently a member of C40 cities which is a network of mayors from nearly 100 cites worldwide who pledge to halve the emissions of their respective cities while improving equity, and building resilient, healthy communities. In addition to this, Mayor Bowser pledged to make the District carbon neutral and climate resilient by 2050. The District also released the Climate Ready DC Plan, which lays out how the District is preparing for and adapting to climate change. DOEE is also in the process of implementing many portions of the 2018 Clean Energy Omnibus Act that was passed by the District Council. DOEE’s Air Program remains interested in energy sector opportunities to reduce GHG emissions because of air quality co-benefits.

According to the EPA, environmental justice (EJ) is the "fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income, with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies." Despite improvements in air quality over recent decades, air pollution is still unevenly and inequitably distributed across the District. For example, Castillo et al. (2021) reported that higher PM _2.5 -attributable disease burdens were found in neighborhoods with larger proportions of people of color, lower household income, and lower educational attainment in the District.

The District's Office of People’s Council (OPC) worked to create a proposed DC-specific EJ community definition drawing which drew upon the EJ community definitions used in NJ, NY, and PA. OPC defined an EJ community as any census tract that meets both of the following criteria: 20% or more of the population lives at or below the federal poverty line and 60% or more of the population identifies as a race other than non-Hispanic/Latinx white.

DOEE's Air Quality Division is on the cutting edge of air quality research. We have the following ongoing research projects/studies with several universities and organizations:

• Collocation studies of low cost sensors with DOEE's federally mandated regulatory monitors (Howard University/George Washington University).
• Study of VOC emissions from cannabis facilities.
• Hyperlocal monitoring in several EJ communities.
• Inequities in PM _2.5 -attributable health impact throughout the District (George Washington University).

DOEE's Air Quality's Division works diligently to improve air quality in the District. There has been significant progress despite a steady growth in population, employment and vehicle miles travelled. However, more work can be done. To briefly summarize:

• Ozone: The District and the metropolitan region have returned to a marginal nonattainment status of the 2015 8-hour ground-level O ₃  NAAQS. Maintaining healthy O ₃  levels continue to be a challenge for the region. Controlling emissions from mobile sources and working with upwind states/regions to address transported pollution are necessary to improve public health.
• CO: The District is in attainment for 2010 8-hour and the 1-hour NAAQS. Ambient air quality levels have been below the standards since 1996.
• Particulate Matter: The District is in attainment of the 2012 annual PM _2.5  NAAQS and the 24-hour NAAQS value. The monitored levels have been below the standards for the past two decades, although more work is needed to address PM hotspots throughout the city.
• SO ₂  and NO ₂ : The District continues to be well within attainment of the SO2 NAAQS and the NO2 NAAQS.
• Lead: The District is in attainment of the 2008 NAAQS. Due to levels being consistently low (at approximately 3% of the NAAQS), the District discontinued measuring lead at the McMillan site.

DOEE is committed to protecting the health and welfare of the District's residents, visitors, and natural environment by reducing ambient pollution levels. Efforts will persist to address air quality issues in the District as the EPA continues to revise the NAAQS and additional pollution control programs.