00:00But let's move on now to the other big story we are tracking this time it is about Delhi's air
00:04and yes I know it's a monsoon but I've got news for you.
00:08Delhi's air is doing something strange this monsoon and most people have understood the science all backwards.
00:16We were taught that rain cleans the air. More rain, more moisture, cleaner lungs, that is true but only half
00:25the truth.
00:26This past week in Delhi proved both sides the story within three days.
00:31Let's start with 9th of July. Delhi recorded an AQI of 39.
00:37Good air, green. Wow, time to celebrate.
00:40Something this city does not see very often. At least we haven't seen it since September of 23.
00:49Safdarjung weather station logged over 72mm of rain in a single day. Real, heavy, sustained rainfall.
00:58But three days later, on 12th of July, the AQI jumped to 261.
01:05You're back in not just moderate but poor air quality.
01:10The worst reading we saw in 85 days.
01:15Same city, same monsoon season. The gap of just about three days.
01:23So what changed?
01:25See, the rain stopped.
01:28And when rain stops in Delhi, the ground is still wet, the air is still humid, but nothing is being
01:33washed away anymore.
01:34Add to that the gusty winds moving about 20-25 km an hour, and those winds start doing the opposite
01:41of what the rain does.
01:42They kick up the dust sitting on the roads and construction sites and carry it straight back into the air.
01:49That is dust.
01:51Remember summer pollution? I explained to you how PM10 was more deadly.
01:56And now here is a part doctors will find useful for patients asking about lungs and allergies.
02:01Delhi's fine pollution particles are unusually reactive to moisture.
02:08Research has found that air here carries high chloride content.
02:12Largely from biomass burning, chloride grabs water aggressively, remember.
02:16And in humid air, these particles absorb moisture and physically swell.
02:22Sometimes getting heavier, larger by about 15-25%.
02:26And what happens during winter?
02:28This swelling makes pollution measurements understate the real problem.
02:36I guess how much?
02:38About 20%.
02:39Because humidity is high, rain is absent to wash the chloride away.
02:44And there you go.
02:46Now during monsoon, the same chloride gets flushed out repeatedly by heavy rain.
02:51So the particles that remain are smaller, lighter, less reactive to moisture.
02:55They are the real reason why monsoon air can be genuinely clean.
02:59Not just wet.
03:01You know, imagine like a good monsoon shower and you can see as far as the Yamuna.
03:07In Noida or in Delhi.
03:09But this only works when rainfall is heavy and frequent.
03:14But what's been happening lately?
03:16A light drizzle does not clear the air.
03:18It does the opposite.
03:20A weak rain adds moisture without the force to wash particles down and out.
03:26Those particles swell in that moisture and hang in the air longer, not shorter.
03:31The real rule for you and me to understand, it is not rain versus no rain.
03:37It is not heavy rain versus weak rain.
03:39It is heavy sustained rain with wind.
03:43The only combination that actually clears out the air and gives some respite to our lungs.
03:49Some respite to our children.
03:50Anything less and the humidity works against us, against our lungs, against our life.
04:00That is why your AQI app can show good air on morning, poor air three days later, without a single
04:06stubble warning, without a single new factory and with the same monsoon season.
04:14So if you're taking away anything from the story, take away this.
04:18Pollution is a real-time threat to your and my life.
04:22It is a real-time threat in the summer, in the winter and now also in the monsoon.
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