Air pollution consists of microscopic solid particles and liquid droplets suspended in the atmosphere, known collectively as particulate matter (PM). This pollution is categorized by size: \(\text{PM}_{10}\) refers to coarse inhalable particles 10 micrometers or less in diameter, and \(\text{PM}_{2.5}\) describes fine particles 2.5 micrometers or less. \(\text{PM}_{2.5}\) is concerning because its small size allows it to penetrate deep into the lungs and enter the bloodstream, affecting nearly every organ system. Exposure reduction strategies must target both outdoor sources, like vehicle exhaust and industry, and indoor contaminants, which accumulate from external infiltration and internal generation.
Reducing Exposure During Outdoor Activities
Minimizing exposure to outdoor air pollution begins with monitoring local conditions, typically reported through the Air Quality Index (AQI). The AQI categorizes air quality from “Good” (0-50) to “Hazardous” (301+), providing a clear indicator for adjusting outdoor plans. Vulnerable populations should reduce or avoid outdoor activity when the AQI reaches moderate levels (51-100) or higher.
The timing and location of outdoor exercise are significant factors in reducing the inhaled dose of pollutants. Avoiding high-traffic periods, such as morning and evening rush hours, substantially lowers exposure to vehicle emissions. Since ground-level ozone typically peaks in the afternoon during summer, an earlier workout time is preferable in warmer months.
Choosing low-traffic routes, such as parks or residential streets, over busy main roads is an effective strategy, as pollution concentrations drop significantly just one or two meters away from major traffic arteries. During periods of extremely poor air quality, such as wildfire events, the proper use of a well-fitted N95 or FFP2 mask can reduce the amount of particulate matter inhaled.
Improving Indoor Air Quality Through Mechanical Systems
High-efficiency filtration systems are the primary mechanical defense against airborne contaminants infiltrating the home. Portable air purifiers equipped with High-Efficiency Particulate Air (HEPA) filters are effective because they are certified to remove at least 99.97% of particles 0.3 micrometers in diameter. These filters are highly efficient at capturing fine \(\text{PM}_{2.5}\) and bacteria.
The central heating, ventilation, and air conditioning (HVAC) system can be upgraded by replacing standard filters with those having a higher Minimum Efficiency Reporting Value (MERV). Residential filters rated MERV 11 to MERV 13 are highly effective, capturing smaller particles like mold spores and smoke. Selecting a filter with too high a rating, such as MERV 14 or above, can restrict airflow and potentially strain an older HVAC system, so compatibility should be confirmed with a professional.
For tightly sealed, energy-efficient homes, controlled mechanical ventilation is necessary to ensure a continuous supply of fresh air. Heat Recovery Ventilators (HRVs) and Energy Recovery Ventilators (ERVs) continuously exhaust stale indoor air and bring in fresh outdoor air. These systems transfer heat between the two airstreams to minimize energy loss; ERVs also manage humidity transfer, which helps prevent moisture-related issues like mold growth.
Sealing the building envelope is a foundational step that prevents the uncontrolled infiltration of unfiltered outdoor air. Air leakage occurs through cracks and gaps around windows, doors, and utility penetrations, allowing outdoor pollutants, dust, and moisture to enter. Sealing these pathways with caulk, foam, and weatherstripping protects a home’s air quality and maximizes the efficiency of mechanical filtration and ventilation systems.
Eliminating Indoor Sources of Pollution
The most effective method for controlling indoor air quality is preventing the generation of pollutants at the source. Cooking is a significant source of indoor \(\text{PM}_{2.5}\) and volatile organic compounds (VOCs), particularly when using a gas stove. Using an outdoor-venting range hood every time the burners or oven are on is necessary for capturing and exhausting these emissions before they disperse into the home.
Behavioral changes during cooking, such as using back burners closer to the ventilation hood and covering pots, also limit the release of pollutants. Many common household products emit VOCs, including paints, cleaning supplies, aerosol sprays, and scented candles.
Mitigation involves choosing products labeled as low-VOC or no-VOC, such as low-emission paints and furniture. The use of harsh chemical cleaners and aerosols should be minimized, and when they are used, windows should be opened briefly for dilution, provided the outdoor air quality is acceptable. Maintaining indoor humidity below 60% helps prevent the growth of mold and mildew, which are biological sources of particulate matter and allergens.