What is PM2.5 and the AQI?

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Patient Presentation
A 4-year-old male came to clinic with increasing cough and decreased activity for 48 hours. He had known intermittent asthma that was usually triggered by an upper respiratory infection (URI). The coughing had been occurring for a couple of days without concomitant fever or URI symptoms, but he was coughing at night. His mother had been giving him albuterol about 3 times a day which was helpful to the child. She was wondering if she should start giving him his prednisone that they used occasionally.

The pertinent physical exam showed a playful child who was coughing. He had a respiratory rate of 24 breaths/minute, and an oxygen saturation of 94%. HEENT was normal. His lungs had very mild end expiratory wheezing. The rest of his examination was normal.

The diagnosis of an asthma exacerbation was made. “I think you should start the prednisone like you usually do, and remember that you can use the albuterol for difficulty breathing up to every 4 hours. But if he really needs it more often than 4 hours please call me. I don’t think this is because of a cold, and with the poor air quality because of the Canadian wildfires I wonder if that is bothering him. Has he been inside since the air quality has been bad?” the pediatrician asked. “I have been keeping him mainly inside but sometimes it’s just too much for him, me and the rest of the family. We’ll go outside for a short time just for a break, but it’s really hard to keep him locked up,” she replied. “I know it is really hard to keep a busy kid cooped up. I’d try to keep him inside as you can. You can use an air purifier if you have one. Also I’d check the filters on your air conditioning system. Make sure they are clean or new and run the house fan. Even if the air conditioning isn’t on, it should circulate the air through the filter. If you can, maybe you can make a mad dash to a friend’s home for a change of scenery. But if he seems like he is getting worse then I want you to call me,” he counseled.

Discussion
Air quality standards are made, measured and monitored by the US Environmental Protection Agency (EPA) through the Clean Air Act. All potential pollutants are not necessarily monitored. Some of the most commonly monitored and studied are fine particulate matter, ground-level ozone, carbon monoxide, nitrogen dioxide, and sulfur dioxide.

Common fine particulate matter < 2.5 µm (PM2.5) sources include the natural sources of biomass burning, coal burning, road and soil dust, sea spray aerosols, wildfire particles, and volcanic dust. Human sources of PM2.5 include residential cooking and heating, farming, fossil fuel combustion, heavy industry, and smoking. Depending on the location, source and other factors, the PM2.5 can be a mixture of hydrocarbons, organic compounds, heavy metals, minerals, ions and biological material.

Studies support both short term and long term health effects of PM2.5 including increased risk of cardiac ischemia and myocardial infarction, arrhythmias, thrombotic events including stroke, exacerbation of asthma, chronic obstructive pulmonary disease, viral infections including bronchiolitis and possibly influenza and COVID-19, and neurodegenerative diseases of the brain including Alzheimer’s, and cancer. For children specifically there is impaired lung development, more asthma, and increased risk of preterm birth and low birth weight.

Impaired lung development is specifically a problem as “…studies suggest that long-term childhood air pollution exposures may shift the entire population distribution of childhood lung function and lung function growth downward…. The consequence …could be lung function that is below the threshold for chronic obstructive pulmonary disease … in later life.” Basically, the lung development is either stunted and never reaches its potential and/or there is earlier decline in lung function because of poor air quality. This is potentially worse if both stunting and early decline were to occur.

“In the US, wildfires have become the #1 single source of PM and contribute more than a third of the total annual burden of PM2.5 in the atmosphere according to the US EPA Emissions Inventory.” Wildfires may be relatively short duration events, but the pollution levels can be quite high and the PM can travel great distances.

Learning Point
The US EPA’s Air Quality Index (AQI) can be found at AirNow.gov which also has local information available.
The AQI is:

  • 0-50 Good
  • 50-100 Moderate
  • 101-150 Unhealthy for sensitive groups
  • 151-200 Unhealthy
  • 201- 300 Very Unhealthy
  • > 300 Hazardous

Good and moderate categories are good times to be outdoors and to air out the house. Reducing exposure risks should be considered for sensitive groups at > 101 and for everyone at > 151. Sensitive groups include anyone with cardiac or pulmonary diseases, children and teenagers, older adults, and people who are more likely to be exposed.

Household interventions to generally improve overall air quality include improved kitchen ventilation, and using clean cookstoves. Air purifiers have been found to help short term respiratory problems for adults and to decrease asthma symptoms, but long-term benefits for children are unknown. Reducing exposure risks can also include decreasing the time spent outdoors, using portable air purifiers, using central HVAC systems if available to circulate and filter air, and decreasing activities which can increase dust and particulates such as dusting, sweeping, using indoor stoves (including gas, propane or wood). Frying foods can also increase indoor particulates. Cloth and surgical type masks do not provide protection for wildfire smoke but N95 masks can offer some protection. The US government recommends being ready for such emergencies such as poor air quality and to have a “clean air room” with increased ventilation and filtration to spend most of one’s time in.

Questions for Further Discussion
1. What are common causes of air pollution in your location?
2. What are environmental hazards in your location?
3. What causes cough? A review can be found here

Related Cases

    Symptom/Presentation: Cough

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for these topics: Air Pollution and Indoor Air Pollution.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Tainio M, Jovanovic Andersen Z, Nieuwenhuijsen MJ, et al. Air pollution, physical activity and health: A mapping review of the evidence. Environ Int. 2021;147:105954. doi:10.1016/j.envint.2020.105954

Garcia E, Rice MB, Gold DR. Air pollution and lung function in children. J Allergy Clin Immunol. 2021;148(1):1-14. doi:10.1016/j.jaci.2021.05.006

Thangavel P, Park D, Lee YC. Recent Insights into Particulate Matter (PM2.5)-Mediated Toxicity in Humans: An Overview. Int J Environ Res Public Health. 2022;19(12):7511. doi:10.3390/ijerph19127511

When Smoke is in the Air. AirNow.gov. Accessed August 1, 2023. https://www.airnow.gov/wildfires/when-smoke-is-in-the-air/

Author
Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa

Published