Protection From Exposure to Particulate Matter Air Pollution: Policies or Personal-level Actions

The increased risk of adverse cardiovascular outcomes from exposure to fine particulate matter (PM2.5) pollution is well-established, both acute effects from short-term exposures to high levels and chronic effects from higher long-term exposures (1). However, strategies to prevent adverse cardiovascular outcomes from PM2.5 exposures have not received either the clinical or policy attention that such exposures deserve based on their relative contribution to global disease burden. As both a physician and a policy maker – I am the Physician Member of the California Air Resources Board -- I am pleased that the American Heart Association commissioned the Scientific Statement on Personal-Level Protective Actions Against Particulate Matter Air Pollution Exposure that is published in this issue (2).

This statement was written before the COVID-19 pandemic and the terrible wildfire season along the Pacific Coast of the United States in the summer of 2020. Both of these disasters provide important context to the valuable information summarized in the document. The early economic shutdown to prevent spread of SARS-CoV-2 infection dramatically reduced air pollution on a global scale, reminding us about how fossil-fueled motor vehicles and power generation foul our air. The widespread use of face masks as an appropriate public health measure to reduce transmission of the virus also may have improved acceptance of wearing masks among the general public in a country like the U.S. where this practice was not common. The prolonged episodes of poor air quality due to multiple large wildfires in Northern California, Oregon, and Washington during the summer of 2020 also appear to have increased public awareness of the potential health impacts of PM2.5.

As bad as the air quality has been along the Pacific Coast of the U.S. due to persistent wildfire smoke, there are millions of people who live in cities where the levels of PM2.5 are just as high on a regular basis, where people spend their entire lives breathing polluted air. Because ambient PM2.5 from all sources is the most important environmental risk factor in the Global Burden of Disease comparative risk assessment, disabling cardiovascular disease and premature death could be prevented with reductions in exposures throughout the world (3).

Given that population growth and economic development are occurring in low and middle-income countries (LMIC), future PM2.5 emissions will be greater due to increased motor vehicle use and coal-fired power generation. Concomitant to this expansion of emissions is increasing global warming that leads to increased need for electricity generation for air conditioning to adapt to the hotter temperatures. Climate change itself is associated with major health impacts (4). The LMIC that will be most impacted by global warming are those which have generated the least amount of greenhouse gases since the industrial revolution.

In the U.S., a disproportionate burden of exposure to PM2.5 falls on the disenfranchised communities (5). These communities are characterized by less health-fostering amenities (e.g., access to healthy foods and green spaces) and more health-damaging factors (e.g., noise and violent crime) that are also a legacy of structural racism. To have the greatest benefit on public health, reductions of exposure to PM2.5 must target these communities.

The Statement in this issue is focused on personal-level actions to reduce exposures to PM2.5. While this is important, it is insufficient. Policies must be developed and implemented to reduce emissions of PM2.5 at sources, primarily motor vehicles and power plants. The U.S. Environmental Protection Agency (EPA) has failed miserably over the last few years to regulate either of these major sources of PM2.5 emissions, and actually moved aggressively to rescind passenger vehicle fuel efficiency (CAFE) standards and the Clean Power Plan that would incentivize states to promote renewable power and close coal-fired plants. Both of these policies were designed to both improve air quality and reduce greenhouse gases to mitigate climate change.

To make the best use of the personal-level actions recommended by the authors of the Statement, better monitoring and forecasting of PM2.5 levels are needed. They discuss the increasing public availability of low-cost monitoring devices and how the data from these devices can be integrated with measurements from air quality monitoring stations used for compliance with regulatory standards. The potential neighborhood-level coverage afforded by widespread use of the low-cost sensors could provide individuals with better information about when to employ personal-level actions to reduce their exposures. The EPA has started to integrate a specific type of low-cost sensor with federally approved compliance monitors to improve reporting of wildfire smoke PM2.5 (6). The EPA’s Air Quality Index (AQI) remains the primary means in the U.S. for disseminating information about public health risks associated with PM2.5 pollution, but only a small proportion of individuals follow the behavioral recommendations associated with each category of the index in non-wildfire conditions. With prolonged poor air quality episodes associated with catastrophic wildfires, public compliance with AQI-associated behavioral recommendations may have improved. In any event, the AQI is only designed to communicate short-term health risks. The authors of the Statement emphasize that tools to communicate about long-term exposures at neighborhood scales are needed to better advise individuals and their health care providers about risks for chronic cardiovascular outcomes.

Because most health care providers lack knowledge about the cardiovascular health risks associated with PM2.5 pollution as well as the personal-level actions that can be recommended to reduce exposures, the Statement is a valuable resource. The recommendations are nicely summarized in Figure 1. Staying indoors with windows closed, creating a clean air room with the use of portable HEPA-filtering air cleaners, and setting a central ventilation system to recirculation mode with a high-efficiency particle filter in place are evidence-based actions that can be taken by individuals during high-level PM2.5 episodes. The authors of the Statement also discuss the evidence for use of N95 respirators, surgical masks, and cloth face coverings for reduction of PM2.5 exposures when individuals have to go outside during bad air quality episodes. Their discussion of the relative degree of protection afforded by each of these types of respiratory personal protective equipment is illuminating, especially their acknowledgement that no evidence suggests wearing a N95 respirator for short durations negatively impacts cardiovascular physiological parameters. Perhaps most importantly, the authors describe gaps in our current knowledge about the effectiveness of various interventions to reduce exposures to PM2.5 on hard cardiovascular outcomes and make recommendations for future research to address these gaps.

In conclusion, the sources of PM2.5 that harm health are the same as those that emit greenhouse gases and climate-forcing aerosols (e.g., black carbon). Because of societal barriers, many individuals in LMIC have disproportionate exposures to PM2.5. To improve public health and mitigate climate change, we need strong policies to move national economies away from reliance on fossil fuels for transportation and power generation as well as to reduce hot spots of exposure in under-represented communities (7,8). Personal-level actions, while important, are not enough.