Inequitable Exposure to Air Pollution from Vehicles in Maryland

, Senior vehicles engineer | November 15, 2019, 1:44 pm EST
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Most people know that cars, trucks, and buses from our highways and city streets are a significant source of harmful air pollution. While this pollution impacts all communities in the state to some degree, Marylanders who face the greatest exposure to transportation pollution are those who live near highways, along major freight corridors, and in urban areas.

Not just that, but the disproportionate distribution of air pollution and its associated health impacts are exacerbated because Maryland has the nation’s second worst air pollution from cars, trucks and buses, after New York State. California follows, with an average that is practically the same as Maryland’s.

To help understand exactly which communities bear the greatest burden and breathe the highest concentrations of this dangerous air pollution, we used a model to estimate the amount of fine particulate matter air pollution (known as PM2.5) produced by on-road vehicles that burn gasoline and diesel. The findings, which are not likely not to be a surprise to many residents, are quite troubling – they show that people of color are disproportionately exposed to vehicular PM2.5.

What is PM2.5 and why is it so important?

The science is clear: no level of particulate matter is safe to breathe, says the American Lung Association. Although PM2.5 is not the only air pollutant that adversely affects health, it is estimated to be responsible for approximately 95 percent of the global public health impacts from air pollution. Exposure to this dangerous pollutant is the largest environmental risk factor in the US, responsible for 63 percent of deaths from environmental causes.

PM2.5 include particles smaller than 2.5 millionths of a meter in diameter – at least 20 times  smaller than the diameter of fine human hair— so they can penetrate deeply into the lungs. The ultrafine particles – smaller than 0.1 millionths of a meter – are particularly dangerous, as some can enter into the bloodstream.

Chronic exposure to PM2.5 causes increased death rates attributed to cardiovascular diseases, including heart attacks and strokes, and has been linked to other adverse impacts such as lung cancer, reproductive and developmental harm and even diabetes and dementia. Chronic exposure to PM2.5 in children has also been linked to slowed lung-function growth and the development of asthma.

PM2.5  is formed in many ways. A significant source of PM2.5  is fuel combustion. The combustion engines of cars burn gasoline and diesel. Power plants burn natural gas and other fuels to produce electricity. Burning wood for cooking and in fireplaces, as well as  wildfires, are examples of biofuel combustion. Not only does burning fossil fuels and biofuels produce PM2.5 directly, but the combustion reaction also emits gases such as nitrogen oxides, sulfur dioxide and volatile organic compounds that go on to form additional PM2.5 through complex chemical reactions in the atmosphere.

Greater pollution for people of color

The results are clear: PM2.5 pollution burden from cars, trucks, and buses is inequitably distributed among racial and ethnic groups in the state. People of color experience an undeniable “pollution disadvantage.”

We estimated exposure to PM2.5 pollution using a recently developed model from the University of Washington, and data from the EPA’s National Emissions Inventory and the US Census Bureau. This model allows us to calculate how vehicle tailpipe and refueling emissions ultimately lead to ground-level pollution exposure, so we can understand how exposure to PM2.5 varies among groups and locations.

The health impacts caused by PM2.5 depend not only on the concentration of pollution, but also on the number of people exposed. A high level of exposure in a densely populated area will have a great public health impact compared to that same exposure in a less densely populated area. Therefore, in order to compare exposure in different areas and groups, our estimates are “population-weighted” PM2.5 concentrations.

Looking at the state as a whole, African Americans are exposed to 12 percent higher PM2.5 concentrations from on-road transportation than the average PM2.5 exposure for all Marylanders.  Latinos experience concentrations 11 percent higher than the average resident (Figure 1).  At the same time, white residents have an average exposure that is 8 percent lower than the average for the state.

Figure 1. Disproportionately High PM2.5  Exposure for African Americans and Latino residents in Maryland

We can look at this data differently by examining the demographics of the cleanest and the most polluted areas. In an equitable world, one might expect that every area with the same pollution level would have an approximately equal representation of all racial groups. In other words, the burden would be shared equally. But this is not the case.

In the cleanest areas of Maryland, in census tracts with average annual PM2.5 concentrations less than half the state average, white residents make up 76 percent of the population, while making up only 52 percent of the state’s total population. In contrast, the most polluted census tracts have a higher proportion of people of color. Almost 15 percent of people in the highest burden areas – where concentrations are more than 1.5 times the state average – are Latinos, compared with a state population that is just 9 percent Latino (Figure 2). People of color are over-represented in the more polluted areas, and under-represented in the less polluted areas.

Figure 2. PM2.5 Unequal Exposure in Different Pollution Areas
Columns show the fraction of people belonging to each of 8 racial groups living in areas with different pollution levels (least polluted on the left, most polluted on the right). The 0–50% area refers to census tracts where PM2.5 pollution is less than half the state average, the 50–100% area refers to tracts where pollution is from half the state average to the state average, etc. The far right column shows the state’s average racial composition.

Furthermore, PM2.5 exposure varies greatly within Maryland. Baltimore City (the county) is exposed to the worst pollution levels, with an exposure that is 37 percent higher than the state average, followed by Prince George’s County with an exposure that is 23 percent higher than the state average. These two counties are home to more than one quarter of the state’s population, which means that more than 1.5 million people are affected by this high level of fine particulate matter from cars, trucks and buses.

For the sake of comparison with pollution levels in California, which has some of the highest levels of vehicular PM2.5 in the nation, the average pollution levels in the county of Baltimore City are only 15 percent lower than the levels in Los Angeles County and are 5 percent higher than San Bernardino County’s levels. The average exposure level in Los Angeles County is double the nation’s average, and in the county of Baltimore City the average exposure isn’t far from that, at 1.8 times the nation’s average.

Figure 3. PM2.5 Exposure Varies Greatly in Maryland

The analysis also shows that less affluent households have a higher exposure to air pollution than more affluent households, although this disparity is not as pronounced among income brackets as it is among racial and ethnic groups.

Our analysis shows that the share of low-income households is disproportionately larger in more polluted areas, where pollution is more than 1.5 times the state average. Statewide, just 11 percent of households earn up to $20,000 per year, but a larger share of these households – 19 percent – are located in these more polluted areas. A similar trend is seen for households in the next income bracket, $20,000 to $60,000, as the number of households in this bracket also increases along with the pollution levels.

As expected, the trend is reversed for households in the highest income brackets, over $100,000 per year. For the state as a whole, 60 percent of households are in these highest income brackets, but just 46 percent of these households are in the most polluted areas.

What is to be done?

The state’s economy is growing, Marylanders continue to buy cars and drive more, and there are more and more freight trucks on our highways. Together, cars, trucks and buses are responsible for the vast majority of our climate transportation emissions – 70 percent of the state’s greenhouse gases from transportation come from gasoline vehicles and 19 percent come from diesel vehicles. Many local air pollutants are co-emitted along with climate-damaging greenhouse gases, and so local air pollution and climate pollution grow hand-in-hand.

While residents can make a difference for local air pollution (as well as for climate emissions) by choosing cleaner vehicles and driving less, much of today’s air pollution comes from sources outside the direct control of individuals. Maryland needs regulations, incentives, and other policies to reduce vehicle emissions. Inequity also needs to be addressed with equal urgency, so the meaningful involvement of affected communities are key considerations in designing policies and strategies to reduce pollution from vehicles.

Maryland is committed to reducing the states greenhouse gas emissions by 40 percent by 2030, which will require significant reductions in emissions from transportation. It is good news that the state recently released a Draft Plan defining a set of at least 100 strategies for reducing the state’s global warming emissions (2019 Greenhouse Gas Reduction Act Draft Plan). One core program in the Draft Plan is a commitment to continue to work with California and other states which have adopted California’s stricter vehicle emission standards. Maryland adopted the California Zero Emission Vehicle (ZEV) standard, which requires automakers to increase the percentage of ZEVs (such as plug-in hybrids and battery electric vehicles) sold in the state. The electrification of vehicles, both passenger and freight, can greatly reduce emissions. Battery-electric vehicles have no tailpipe emissions and they eliminate emissions associated with gasoline refueling.

At the end of last year, Maryland joined eight other states and the District of Columbia in a regional effort to develop a regional market program to address transportation emissions. Known as the Transportation and Climate Initiative (TCI), this program will provide much-needed funding to implement clean transportation strategies, and it is also one of the avenues towards reducing pollution exposure inequity. But in order to adequately address the disproportionate impact of pollution, the state should seek input specifically from overburdened communities.

Inequity in air pollution reflects decades of local, state, regional, and national decisions about transportation, housing, and land use. Decisions concerning where to construct highways, where to invest in public transportation, and where to build housing have all contributed to a transportation system that concentrates emissions in communities of color. With the inclusion of affected communities in the decision-making processes of the programs listed in the Draft Plan, Maryland is being handed an opportunity to address the consequences of decades of decisions.

Other specific actions included in the Draft Plan are important to reduce air pollution and its inequitable distribution. Some of these are:

  • A transition to cleaner and more efficient public transportation fleets, as well as the expansion of public transportation.
  • A pilot program of electric school buses has been approved. It needs to focus on serving communities exposed to the highest levels of gasoline and diesel emissions.
  • Expansion of electric vehicle rebate programs to provide financing assistance and larger rebates to low- and moderate-income residents, as well as excise tax credits for the purchase of plug-in vehicles.
  • Utility investments in electric vehicle charging infrastructure, with a priority on serving communities exposed to the highest levels of gasoline and diesel emissions.
  • Time-of-use rates which allow utility customers to charge during off-peak hours at a reduced energy rate.

Air pollution from on-road transportation such as diesel and gasoline vehicles places significant, inequitable and unacceptable health burdens on Maryland residents. We have the tools and the technologies to transform our transportation system away from diesel and gasoline and toward clean, modern, and equitable solutions. However, state leadership is critical, especially at a time when the federal government is rolling back federal fuel economy and greenhouse gas emissions standards for passenger cars and light trucks.

Maryland needs to continue the effort to reduce air pollution from vehicles, placing a high priority on actions that reduce the inequitably distributed burden of air pollution in the state. This air quality analysis provides important quantitative evidence of the need for and importance of such programs, and it can help inform and shape future actions to reduce on-road transportation pollution exposure and inequities in the state.

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