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Walking home after a Tuesday storm in Vienna, the air smelled like wet stone and crushed leaves. That familiar after-rain scent isn’t a fantasy; it has a name — petrichor — and it turns up when rain hits dry ground, flicking tiny droplets carrying plant oils and a compound called geosmin into the air.

This piece is a short, practical guide: what rain does clean, what it doesn’t, and how to make use of those fresher-feeling hours after a shower.

The short version

• Rain does clean the air. Falling drops collide with dust, pollen, soot and other particles and bring them down — a process called washout.
• Bigger, steadier rain works best. A sustained shower with larger drops removes more particles than drizzle.
• Some pollution lingers. Gases such as ozone and nitrogen oxides don’t “wash out” as efficiently and can behave oddly around storms.
• Enjoy it, but check the numbers. If you have a low‑cost sensor or AQI app, you’ll often see a dip in PM₂.₅ during and after rain — but results vary by place and weather.

How raindrops “vacuum” the sky

Each drop acts like a moving net. As it falls, it sweeps up airborne particles — particularly coarse dust and pollen, and a fair share of fine particles (PM₂.₅). The physics is simple: more collisions mean more capture. That’s why heavy, persistent rain tends to show the most obvious improvement in local particle readings.

You can often feel this indoors too. Crack a window for ten minutes after the main shower passes and outdoor readings improve; you’ll refresh indoor air without inviting in a blast of humidity.

What rain doesn’t fix

Rain isn’t a universal reset button:

• Gaseous pollutants (e.g. ozone, NOₓ) aren’t removed nearly as well by washout. Around thunderstorms, ozone chemistry can be complex, and levels don’t always fall just because it rained.
• Light, brief showers may barely dent wildfire smoke or busy-road pollution.
• Re‑entrainment happens. Once surfaces dry, traffic and wind can kick some dust back up. And stormwater washes grime into drains rather than removing it from the environment entirely.

Petrichor: that after‑rain smell

• What you’re smelling: a mix of plant oils and geosmin from soil bacteria, aerosolised by raindrop impacts.
• Why it feels so fresh: you’re getting both a scent cue and (often) a real drop in particle counts — a nice one‑two for the senses.

About those “negative ions”

Storms and waterfalls can increase negative air ions, and people often report the air feels clearer or their mood lifts. The evidence is suggestive but not definitive. It’s fine to enjoy the effect; just don’t treat it as a guaranteed health intervention.

Make the most of rainy clean‑ups

• Time your ventilation. If outdoor PM₂.₅ dips after a shower, ventilate briefly to swap indoor air.
• Use data, not hunches. A portable monitor or your local AQI feed will show what changed where you live.
• Mind the rebound. Conditions can return to “pre‑rain” within hours in traffic‑heavy areas, especially once roads dry.

Bottom line

Rain is nature’s free, city‑wide particle scrubber — not a cure‑all. Enjoy the petrichor, take advantage of cleaner windows of time after sustained showers, and keep an eye on the numbers to know what’s really happening in your neighbourhood.

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Want to track how rain affects your local air quality? Check out our portable air monitor guide to see the difference for yourself.