1 00:00:01,920 --> 00:00:06,480 Speaker 1: Welcome to Brainstuff, a production of I Heart Radio. Hey 2 00:00:06,600 --> 00:00:10,480 Speaker 1: rain Stuff Lauren Bolga Bam here. Most people notice a 3 00:00:10,560 --> 00:00:14,640 Speaker 1: distinctive smell in the air after it rains. It's frequently 4 00:00:14,680 --> 00:00:17,639 Speaker 1: linked with spring, as the smell of fresh cut grass 5 00:00:17,760 --> 00:00:20,600 Speaker 1: is associated with summer. You'll find it in a lot 6 00:00:20,640 --> 00:00:24,000 Speaker 1: of poetry and also on lots of inspirational lists of 7 00:00:24,040 --> 00:00:27,200 Speaker 1: things to be happy about. The scientific name for it 8 00:00:27,360 --> 00:00:30,440 Speaker 1: is petrochor, and it was first named by two Australian 9 00:00:30,480 --> 00:00:34,159 Speaker 1: researchers in the nineteen sixties, and it actually comes from 10 00:00:34,159 --> 00:00:38,240 Speaker 1: the moistening of the earth by rain. But what exactly 11 00:00:38,360 --> 00:00:42,680 Speaker 1: causes the scent? As it turns out, the smells that 12 00:00:42,720 --> 00:00:45,880 Speaker 1: people associate with rainstorms can be caused by a number 13 00:00:45,920 --> 00:00:49,080 Speaker 1: of things. One of the more pleasant rain smells, the 14 00:00:49,120 --> 00:00:52,040 Speaker 1: one we often notice in the woods, is caused by 15 00:00:52,320 --> 00:00:57,760 Speaker 1: bacteria actino my seats, is a genus of filamentous bacteria 16 00:00:57,880 --> 00:01:01,560 Speaker 1: that grow in soil when conditions are damp and warm. 17 00:01:01,720 --> 00:01:05,119 Speaker 1: When the soil dries out, the bacteria produce spores around 18 00:01:05,160 --> 00:01:09,399 Speaker 1: themselves for protection. The wetness and force of rainfall kick 19 00:01:09,520 --> 00:01:12,400 Speaker 1: these tiny spores up into the air, where the moisture 20 00:01:12,440 --> 00:01:15,200 Speaker 1: After a rain acts as an air sol like an 21 00:01:15,240 --> 00:01:18,840 Speaker 1: air sool air freshener. The moist air easily carries the 22 00:01:18,880 --> 00:01:22,000 Speaker 1: spores to us so that we breathe them in. These 23 00:01:22,040 --> 00:01:25,360 Speaker 1: spores have a distinctive earthy smell that we often associate 24 00:01:25,480 --> 00:01:30,480 Speaker 1: with rainfall. The actual compound responsible for the smell is 25 00:01:30,520 --> 00:01:34,440 Speaker 1: called geosmin, which is released by the bacteria as they die. 26 00:01:35,360 --> 00:01:38,240 Speaker 1: Geosmin is a type of alcohol molecule and has a 27 00:01:38,360 --> 00:01:42,240 Speaker 1: very strong scent. The bacteria are extremely common and can 28 00:01:42,280 --> 00:01:44,959 Speaker 1: be found in areas all over the world, which accounts 29 00:01:44,959 --> 00:01:48,320 Speaker 1: for the universality of this sweet after the rain smell. 30 00:01:49,400 --> 00:01:52,440 Speaker 1: Since the bacteria thrive in moist soil but release the 31 00:01:52,480 --> 00:01:55,400 Speaker 1: spores once the soil dries out, the smell is most 32 00:01:55,400 --> 00:01:58,480 Speaker 1: acute after a rain that follows a dry spell, although 33 00:01:58,520 --> 00:02:03,080 Speaker 1: you'll notice it to some degree to most rainstorms. Another 34 00:02:03,120 --> 00:02:05,720 Speaker 1: sort of smell is caused by the acidity of rain. 35 00:02:06,560 --> 00:02:09,520 Speaker 1: Because of compounds in the atmosphere, rainwater tends to be 36 00:02:09,600 --> 00:02:13,640 Speaker 1: somewhat acidic, especially in urban environments. When it comes in 37 00:02:13,720 --> 00:02:17,320 Speaker 1: contact with organic debris or compounds on the ground, it 38 00:02:17,360 --> 00:02:22,160 Speaker 1: can cause some particularly aromatic reactions. It breaks apart soil 39 00:02:22,280 --> 00:02:26,679 Speaker 1: and releases minerals trapped inside, which react with chemicals like gasoline, 40 00:02:26,720 --> 00:02:31,120 Speaker 1: giving them a stronger smell. These reactions generally produce more 41 00:02:31,200 --> 00:02:35,160 Speaker 1: unpleasant smells than bacteria spores, which is why the after 42 00:02:35,200 --> 00:02:38,519 Speaker 1: the rain smell isn't always a nice one like the 43 00:02:38,560 --> 00:02:42,200 Speaker 1: smell caused by bacteria spores. The smell of chemical reactions 44 00:02:42,320 --> 00:02:45,200 Speaker 1: is most noticeable when it rains following a dry spell. 45 00:02:45,880 --> 00:02:48,160 Speaker 1: This is because once the chemicals on the ground have 46 00:02:48,240 --> 00:02:51,560 Speaker 1: been diluted by one downpour, they don't have as strong 47 00:02:51,639 --> 00:02:57,040 Speaker 1: of or as many reactions with new rainwater. Another after 48 00:02:57,080 --> 00:03:00,160 Speaker 1: the rain smell comes from volatile oils that plants and 49 00:03:00,240 --> 00:03:04,080 Speaker 1: trees release. The oil then collects on surfaces such as rocks. 50 00:03:04,760 --> 00:03:06,919 Speaker 1: The rain reacts with the oil on the rocks and 51 00:03:07,040 --> 00:03:10,200 Speaker 1: carries it again as a gas through the air. This 52 00:03:10,400 --> 00:03:13,880 Speaker 1: scent is like bacterious bores in that most people consider 53 00:03:13,919 --> 00:03:17,480 Speaker 1: it a pleasant and fresh smell. It's even been bottled 54 00:03:17,480 --> 00:03:22,000 Speaker 1: and sold for its aromatic qualities. These are a few 55 00:03:22,160 --> 00:03:24,960 Speaker 1: common rain smells, but there are also all sorts of 56 00:03:24,960 --> 00:03:28,280 Speaker 1: other scents after it rains. There are lots of aromatic 57 00:03:28,360 --> 00:03:31,760 Speaker 1: materials that the moisture and impact of rain can stir up, 58 00:03:32,160 --> 00:03:36,000 Speaker 1: and the moist atmosphere following a downpour is particularly good 59 00:03:36,000 --> 00:03:39,120 Speaker 1: at carrying these particles through the air and into our noses. 60 00:03:40,000 --> 00:03:42,680 Speaker 1: So when you talk about the after the rain smell 61 00:03:42,760 --> 00:03:45,560 Speaker 1: with a friend, you may mean one thing while they're 62 00:03:45,560 --> 00:03:54,440 Speaker 1: thinking of something else entirely. Today's episode is based on 63 00:03:54,480 --> 00:03:57,680 Speaker 1: the article what causes petroc or the earthy smell after 64 00:03:57,760 --> 00:04:01,640 Speaker 1: rain on how stuffworks dot Com, written Katherine Whitburn. Brain 65 00:04:01,640 --> 00:04:04,000 Speaker 1: Stuff is production by Heart Radio in partnership with how 66 00:04:04,040 --> 00:04:06,400 Speaker 1: stuff works dot Com and is produced by Tyler Clain. 67 00:04:06,880 --> 00:04:09,200 Speaker 1: For four more podcasts. For my heart Radio, visit the 68 00:04:09,280 --> 00:04:12,000 Speaker 1: I heart Radio app, Apple Podcasts, or wherever you listen 69 00:04:12,040 --> 00:04:13,000 Speaker 1: to your favorite shows.