Yes, rain can improve air quality, but only temporarily. Rainfall washes some airborne particles out of the air through a process called wet deposition, so AQI often drops during and after a downpour. It does not stop pollution sources, so levels rise again once the rain ends.
In July 2025, Delhi recorded its cleanest July in 10 years, with a monthly average AQI of 79 through 30 July, helped by rain on 23 of 31 days, according to CPCB data reported by India TV.
The catch: relief this short is not a fix. Here is what rain really does to air quality, what it can't do, and why post-rain readings can mislead.
The Mechanism
How Does Rain Improve Air Quality?
Rain lowers airborne pollutant levels mainly through wet deposition, also called washout. Falling raindrops capture suspended particles and carry them to the ground.
Not every particle clears equally. Studies find that rain removes larger particles such as PM10 more readily than fine PM2.5 (Liu et al., 2020), and that more intense rain removes more than lighter rain (Beijing rainfall study). Light drizzle can even push PM2.5 readings up in humid conditions. Wind matters too, because it decides whether polluted air is mixed, diluted or brought back in from elsewhere.
Then comes the rebound. Vehicles, industry, construction and combustion don't pause for the weather. Once the rain stops, concentrations can climb again. A clean reading right after rain describes conditions at that moment, not the end of pollution.
Definitions
What is Air Quality & How It's Measured?
Air quality describes how clean or polluted the air is, based on the concentration of pollutants in it.
To measure it, scientists use the Air Quality Index (AQI). The AQI is a score that converts measured pollutant concentrations into a single number. The higher the AQI, the more polluted the air.
AQI is calculated from pollutants like:
PM2.5 — tiny particles that enter your lungs and bloodstream
PM10 — dust and larger particles
Nitrogen dioxide (NO₂)
Sulfur dioxide (SO₂)
Carbon monoxide (CO)
Ozone (O₃)
People often check air quality today on apps or government websites to know whether it's safe to go outside.
Root Causes
Why Air Quality is Bad in India?
India is home to some of the most polluted cities in the world, driven by a mix of human activity and natural factors.
Vehicle Emissions
With millions of vehicles on the road, nitrogen oxides and carbon monoxide flood the air daily.
Industrial Pollution
Coal-based power plants and factories release massive amounts of particulate matter.
Stubble Burning
Seasonal burning of crop residue in Punjab and Haryana adds smoke to already polluted skies.
Construction Dust
Rapid urbanization means constant construction, contributing to PM2.5 and PM10 levels.
Weak Enforcement
Environmental laws exist, but on-ground implementation is often lacking.
So while rainfall helps temporarily, the root causes of India's bad air quality remain constant.
Health Impact
Can Air Quality Make You Sick?
Yes. Exposure to air pollution is linked to short-term and long-term health effects, especially from particulate matter.
Short-Term Effects
- Coughing
- Eye irritation
- Headaches
- Fatigue
Long-Term Effects
- Asthma
- Lung cancer
- Heart disease
- Reduced life expectancy
Did you know? The WHO estimates that ambient (outdoor) and household air pollution together are associated with about 7 million premature deaths each year. Outdoor air pollution alone accounts for an estimated 4.2 million.
Even moderate AQI levels can affect children, the elderly and pregnant women.
Measurement
Are Air Quality Monitors Accurate?
Air quality monitors are useful, but readings vary by monitor type and conditions.
You may have noticed different AQI numbers on various apps and wondered, "Which one is right?" Here's the truth:
Government Monitors
Very accurate, but fewer in number. They are considered the gold standard but may not cover every location.
Low-Cost Sensors
More widespread and affordable, but can be slightly off due to weather conditions like humidity or temperature changes.
The key is not to obsess over small differences. Two apps can show 180 and 200 for the same hour. Both fall in the Moderate band on India's AQI scale (below), so read the band, not the exact number. If the band is Poor, Very Poor or Severe, treat the air as unsafe whichever app you check.
Sensor Behavior
Why Can Rain Affect Sensor Readings?
Humidity is a documented source of error for some low-cost optical particle sensors. US EPA researchers found that raw readings from a widely used low-cost sensor overestimated PM2.5 by about 40% on average, and that adding a humidity correction reduced the error.
After rain, humidity often stays high, so a low-cost sensor can read differently from a reference monitor. That doesn't make every low-cost sensor wrong. It means one reading taken right after rain is not the full picture.
If you run a factory, commercial building or facility with compliance needs, a consumer sensor is not evidence. Equinox Labs' environmental monitoring gives you measured, documented air quality data.
Reference
What Air Quality is Good?
India's AQI scale runs from Good to Severe, and higher numbers mean poorer air.
| AQI | Category |
|---|---|
| 0–50 | Good (minimal impact) |
| 51–100 | Satisfactory (minor breathing discomfort possible) |
| 101–200 | Moderate (vulnerable groups may feel effects) |
| 201–300 | Poor |
| 301–400 | Very Poor |
| 401–500 | Severe |
Ideally, we all want to breathe in the 0–50 range.
Standards
WHO Air Quality Guidelines
WHO guidelines are health-based recommendations. India's National Ambient Air Quality Standards (NAAQS) are the notified national standards, set separately for annual and 24-hour averages.
The WHO is stricter. According to its 2021 global guidelines:
PM2.5: not to exceed 5 µg/m³ annually, 15 µg/m³ daily
PM10: not to exceed 15 µg/m³ annually, 45 µg/m³ daily
Under CPCB's NAAQS, PM2.5 is capped at 40 µg/m³ (annual) and 60 µg/m³ (24-hour), and PM10 at 60 µg/m³ (annual) and 100 µg/m³ (24-hour).
Now compare that to Delhi. In winter 2024-25, the Anand Vihar station averaged 227 µg/m³ of PM2.5, and the city's daily PM2.5 peaked at 602 µg/m³ on 18 November 2024, according to the Centre for Science and Environment. Mumbai's winter average was about 50 µg/m³. Clearly, we have a long way to go.
Setting the Record Straight
Myths vs Facts About Rain and Air Pollution
Rain can improve outdoor air quality, but the improvement is conditional and temporary.
Myth
Rain permanently improves air quality, and a good AQI after rain means pollution is gone.
Fact
It's temporary. AQI improves during rainfall but can bounce back. Pollutants re-accumulate as soon as sources continue.
Myth
Heavy rain means zero pollution.
Fact
Heavy rain reduces some airborne particles but doesn't guarantee clean air. Mumbai's PM2.5 typically bottoms out in the monsoon, yet traffic, construction and industry keep emitting, and levels climb again in winter.
Myth
If outdoor air improves, indoor air improves too.
Fact
Not automatically. Indoor air depends on ventilation, humidity, dampness and indoor sources, not on the rain outside.
Case Data
Examples of Rain & Pollution
Beijing: A study of rainfall events found that heavier rain removed pollutants more efficiently than lighter rain, so not all rain cleans equally.
Journal of Meteorological ResearchMumbai: An analysis of six years of data found Mumbai's PM2.5 was highest in winter and lowest in the monsoon months. Monsoon rain brings relief, but the sources stay.
Exceedances and trends of PM2.5 in five Indian megacities Indoors
Does Rain Improve Indoor Air Quality?
Not automatically. Rain can improve outdoor air without improving the air inside a building.
Indoors, ventilation, humidity, dampness, building materials and indoor activities decide air quality. In wet weather, moisture can become the bigger concern. The WHO's review of dampness and mould links damp buildings to more respiratory symptoms, allergies and asthma, and says the most important step is preventing persistent dampness and microbial growth.
Don't assume the outdoor AQI describes the air inside your workplace. Indoor air quality (IAQ) testing measures indoor conditions directly. For more on when and why to test, read our guide on how air quality testing protects your health.
The Bigger Picture
Why Rain Alone Isn't Enough?
The truth is that rain is not a solution; it's just a breather. Pollution sources such as cars, factories and stubble burning don't stop when it rains. As soon as the skies clear, AQI can rebound. That's why we need systemic, long-term changes.
Systemic Fixes
Long-Term Solutions to Improve Air Quality
Cleaner transport: more EVs, less diesel
Stricter emission controls for industries and power plants
Urban greenery: trees act as natural air filters
Personal steps: masks, planting trees, less car use, checking daily AQI
Right Now
Air Quality Today: What You Can Do?
Want to protect yourself right now? Here's how:
Check the AQI daily using apps like AQI India, AirVisual, or CPCB.
Avoid outdoor exercise when the AQI is poor.
Use N95 masks when stepping out on bad air days.
Air purifiers can help indoors.
Remember that you can't control the weather, but you can control how you respond to poor AQI. So, does rain really improve air quality? Yes, but only for a while.
Rain acts like nature's broom, sweeping away pollutants and giving us a short-lived breath of fresh air. But unless we tackle the root causes of air pollution from vehicles, industries and crop burning, we're only waiting for the next shower to save us.
Next time it rains and the air smells fresher, enjoy the moment, but remember: clean air isn't a gift of rain, it's a right we must fight for. What's the AQI in your city today, and how are you protecting yourself from it?
For Facilities
When Should a Business Test Its Air Quality?
When you need evidence, not assumptions. A weather report or a single AQI reading can't tell you what is in the air at your facility. Testing makes sense when you are assessing a facility, investigating a complaint, supporting certification or reviewing environmental controls.
Equinox Labs is an NABL-accredited, FSSAI-notified food, water and air testing laboratory in Navi Mumbai, with 21+ years of experience and a PAN-India presence. Factories, construction sites and civic bodies can check compliance with outdoor air quality testing. Building owners pursuing green certification can use LEED/WELL certification support.
Talk to Equinox Labs About Air Quality Testing
Measured, documented air quality data for your facility — not a consumer sensor reading.
Talk To Our Experts FAQ
Frequently Asked Questions
Yes, temporarily. Rain removes some airborne particles through wet deposition, so AQI often improves during and after rainfall. The effect depends on rainfall intensity, particle size, wind and whether pollution sources keep emitting. A cleaner reading after rain shows conditions at that moment, not permanent removal of pollution.
Raindrops capture suspended particles as they fall and carry them to the ground, a process called wet deposition or washout. How much is removed depends on the pollutant, particle size, rainfall intensity and wind. Different pollutants respond differently, so rain does not clear every pollutant equally.
Partly. Rain can remove some PM2.5, but fine particles are generally harder for raindrops to capture than larger PM10 particles. Light drizzle in humid conditions can even raise PM2.5 readings. Check the PM2.5 reading itself, not only the overall AQI.
There is no fixed duration. It depends on rainfall amount and intensity, wind, atmospheric mixing and whether emission sources continue. Once the rain stops and vehicles, industry and construction keep emitting, pollutant levels can rise again and the improvement can fade quickly.
No. Heavy rain can lower some airborne particles, but it does not guarantee clean air. Different pollutants respond differently, and wind, atmospheric mixing and continuing emissions all affect air quality during and after rainfall. Check the AQI category and pollutant readings instead of assuming.
Not necessarily. Rain changes outdoor conditions, while indoor air quality depends on ventilation, humidity, dampness, building conditions and indoor pollutant sources. Wet weather can add moisture problems such as dampness and mould. Measuring indoor air directly is the only reliable way to know.
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