What is PM2.5 and What Are the Health Risks of PM2.5?
PM2.5 is the term we use for fine particulates in the air that are under 2.5 microns in size. This pollution is from emissions from combustion of gasoline, oil, diesel fuel, or wood. Other things found in the air that qualify as PM2.5 are organic carbon, organic nitrates and sulfates, and other miscellaneous fine particulates that make up smoke and haze. PM10 are larger particles under 10 microns which would include dust, pollen, and fragments of bacteria. PM2.5 is a subset of PM10. We are concerned with both classes of inhaled pollutants but will primarily focus on PM2.5 in this blog. Acute, more intense exposure to PM2.5 has been linked to premature death, especially in people with heart or lung conditions, and reduced lung function in children. The International Agency for Research in Cancer published in 2015 that PM2.5 particulate in outdoor air is a contributor to lung cancer. Many people are familiar with these risks of small particle exposure. However, there are more insidious health issues, particularly in activation and accelerating aging of the immune system, as well as inducing chronic inflammation in the lungs and in the body generally.
How Do We Get Exposed to PM2.5?
It is perhaps easier to imagine in the outdoors how these very tiny particles and chemicals are combusted and present, but most of us spend 90% of our time indoors. How are we affected by outdoor air pollution? Of course, outdoor air can and does come into our homes and workplaces, sometimes deliberately with a fresh air intake installed in an HVAC system or sometimes through doors, windows, and attic vents. Particulate can also come from indoor sources, like packaging, wood fires, smoking, cooking, burning candles, or cleaning. Indoors we also have accumulated dust mites, mold spores, and other allergens that are not properly ventilated out or filtered. The National Ambient Air Quality Standard for PM10 24-hour standard is 150 (µg/m3). The National Ambient Air Quality Standard for PM2.5 24-hour standard is 35 micrograms per cubic meter of air (µg/m3). The annual standard for PM2.5 is 12.0 µg/m3, averaged over three years.
What Happens When We Are Exposed to PM2.5?
The lung contains an army of immune cells along all of its surfaces that come in contact with air. When exposed to very small particulates (PM2.5) some of these immune cells produce Interleukin- 6 (IL-6), which is an inflammatory messenger and signals the entire body’s immune system to activate. PM2.5 also induces responses in other cells responsible for guarding the body against foreign invaders – specialized cells called “antigen-presenting cells” and other types of immune cells that carry a protein called CD86. Long-term exposure to higher PM2.5 reduces the “innate immune system function” in the lung. The innate immune system is our first responder and first line of defense against pathogens. Other authors have documented oxidative stress (damage from inflammation), uncontrolled inflammation, asthma, and eventually lung remodeling (called Pulmonary Fibrosis) which may be irreversible. So, in the short term, we may see increased susceptibility to various pathogens, like flu, RSV, COVID-19, and other pneumonias, as well as more serious symptoms with these same infections. But in the long-term, scientists have documented lung damage and cancer, as well as accelerated aging of the immune system, proven via biomarkers, and confirmed based on the immune footprint they are seeing.
PM2.5 Links to Increased Risk of Autoimmune Disease
We are even seeing an increased risk of autoimmune diseases, such as rheumatoid arthritis. One study documented a 13% increase in autoimmune disease for each 10 ug/m3 incremental increase in PM2.5 over 20. Allergists are seeing an increased risk of food allergies and environmental allergies, both of which are documented to increase with higher PM2.5 exposures. Apparently with higher exposure to particulate and immune activation, not only the lung but also the gut and other linings become somewhat “leaky” and seem to allow in proteins and molecules that would not normally be present in the blood.
The Danger of PM2.5 Is That We Are Likely Unaware
There are two issues I want to point out that really demand our understanding and attention. The danger for all of us is that we may not feel anything in particular, even when we exercise in unhealthy air. For the fittest athletes, bad air may represent an even more severe threat, as no adverse effect during or after the exercise alerts the exerciser that damage is occurring, some of which may be irreversible. A less fit person might tend to feel some shortness of breath, or early fatigue or dizziness. The second issue is even more dangerous – the quality of our indoor air, since we spend most of our time inside. If we didn’t think about ventilation before, COVID certainly brought that issue forward, as it became clear that ventilation mattered, particularly in schools and public spaces.
How Do We Monitor For PM2.5?
For outdoor air quality, in particular the PM2.5 levels, you can download an app, either AirNow (run by the EPA) or IQAir (A private Swiss company that monitors air globally and provides data at no charge). We recommend outdoor exercise only when the code is GREEN or YELLOW, not ORANGE or RED. IQAir also makes and sells monitors for indoor and outdoor air that can communicate with your phone via a connected app. For indoor air, there are many monitors available. Some of the portable filters even come with built-in PM2.5 monitoring. Here is one example of a free-standing typical indoor air monitor: Airknight 9-in-1 monitor, approximately $119 on Amazon.
What Are The Appropriate PM2.5 And Other Target Levels?
What is a “good” PM2.5 in the home air?
The air quality index, or “AQI” converts concentrations for very fine particles to a number on a scale from 0-500. Good AQI corresponds to 50 or less, or 12.0 ug/meter cubed.
What is a “good” Carbon dioxide level in the home?
A well-ventilated home will have 400-1000 ppm. At 2000-5000 ppm many people will have sleepiness, stuffiness, or headaches.
What is a “good” VOC level (volatile organic compounds) in the home air?
The EPA recommends keeping total volatile organic compounds below 0.5 ppm (however the WHO recommends below 0.3 mg per meter cubed (However up to 0.5 mg/m3 is likely ok) however there is no regulation in place for this as of now. LEED guidelines recommend under 0.5 mg/m3 as well. OSHA guidelines are here: https://www.osha.gov/annotated-pels/table-z-1.
Read about symptoms that can occur from elevated VOC levels in the air here: https://www.epa.gov/indoor-air-quality-iaq/volatile-organic-compounds-impact-indoor-air-quality#Health_Effects
What is a “good” formaldehyde (HCHO) level in the home air?
Most toxicologists recommend less than 0.3 ppm in order to avoid eye irritation, less than 0.1 ppm is recommended for more sensitive people. This 0.1 ppm corresponds to 0.12 mg/m3.
We will cover filters and HVAC tips in another blog. For now, monitor your exposures and minimize your risk to maximize your immune function and longevity!
The Impact of PM2.5 On the Respiratory System (Goes over the main three pathways of damage): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4740125/
Effects of Components of PM2.5 Collected in Japan on the Respiratory and Immune Systems: https://journals.sagepub.com/doi/full/10.1177/1091581816682224
Aging and Deaths attributable to ambient PM2.5 pollution… Found 8.2 million excess deaths globally per year in 2016: https://www.thelancet.com/journals/lanplh/article/PIIS2542-5196(21)00131-5/fulltext
Long-term exposure to air pollution and autoimmune diseases: https://rmdopen.bmj.com/content/8/1/e002055
Early life exposure to air pollution associated with food allergy in children: https://www.sciencedirect.com/science/article/abs/pii/S0013935122020400