How Air Quality Affects Your Lungs

Air quality has moved from a niche concern to a normal part of planning your week in much of the world. Here's what the numbers mean and what's worth doing about them.

What's actually in polluted air

Particulate matter is the big one. PM10 refers to particles under 10 micrometres across; PM2.5 to particles under 2.5 micrometres. The size matters enormously, because it determines how deep into the respiratory tract a particle travels. Larger particles are largely caught in the nose and upper airways. PM2.5 reaches the small airways and the alveoli — the tiny sacs where gas exchange happens — and the finest fraction can cross into the bloodstream.

Ozone at ground level is formed when sunlight reacts with vehicle and industrial emissions, which is why it peaks on hot sunny afternoons. It's a direct airway irritant and can cause chest tightness and coughing at surprisingly modest concentrations.

Nitrogen dioxide comes mostly from combustion — traffic and gas appliances. It's a significant indoor pollutant in homes with gas cooking and poor ventilation.

Reading the index

Most countries publish an air quality index that condenses these into one number, usually colour-coded. In the US system, under 50 is good, 51 to 100 is moderate, 101 to 150 is unhealthy for sensitive groups, 151 to 200 is unhealthy for everyone, and higher bands climb from there. Sensitive groups means children, older adults, and people with asthma, COPD or heart conditions.

The practical habit is checking it the way you check the weather before planning outdoor exercise. Exercise increases your ventilation rate several-fold, so a bad-air-day run delivers far more pollutant to your airways than the same time spent sitting outside.

Wildfire smoke specifically

Wildfire smoke is dense PM2.5, and its spread across large regions means people hundreds of miles from any fire now deal with genuinely hazardous air for days at a time. On smoke days: keep windows closed, run a HEPA air purifier in the room you spend most time in, set air conditioning to recirculate, and postpone outdoor exercise rather than pushing through. If you need to be outside for an extended period, a properly fitted N95 does something meaningful — a cloth or surgical mask does not filter fine particulate.

What your body already does

Your airways aren't defenceless. The mucus layer traps particles and cilia sweep them out continuously, and this handles ordinary exposure without you noticing. The system is overwhelmed by sustained high exposure, and it's damaged directly by smoking, which is why smokers fare worse on bad air days.

And what supplements can and can't do

Population research has linked diets high in antioxidant vitamins with slightly less lung function decline in people exposed to pollution. That's observational, the effect sizes are modest, and it concerns dietary patterns over years rather than any specific product. No supplement filters your air. A HEPA purifier and a closed window do considerably more on a smoky day than anything you can swallow.