{"id":4176,"date":"2026-11-14T04:25:30","date_gmt":"2026-11-14T04:25:30","guid":{"rendered":"https:\/\/www.farmersforum.ie\/trends\/nighttime-smoke-from-fires-continues-to-evolve-as-humidity-determines-whether-it-turns-brown-or-breaks-up\/"},"modified":"2026-11-14T04:25:32","modified_gmt":"2026-11-14T04:25:32","slug":"nighttime-smoke-from-fires-continues-to-evolve-as-humidity-determines-whether-it-turns-brown-or-breaks-up","status":"publish","type":"post","link":"https:\/\/www.farmersforum.ie\/trends\/nighttime-smoke-from-fires-continues-to-evolve-as-humidity-determines-whether-it-turns-brown-or-breaks-up\/","title":{"rendered":"Nighttime Smoke from Fires Continues to Evolve as Humidity Determines Whether It Turns Brown or Breaks Up"},"content":{"rendered":"<p>Particles released by wildfires do not stop reacting after sunset. A study from the University of Kentucky, published on October 24, 2026, shows that ambient humidity steers the nocturnal chemistry of a key smoke compound, catechol. This finding matters for estimating the impact of plumes on climate and air quality.<\/p>\n<figure class=\"wp-block-image size-large\"><\/figure>\n<h2 class=\"wp-block-heading\">Catechol, a phenol released by biomass burning, reacts after sunset with the nitrate radical<\/h2>\n<p>The combustion of biomass emits numerous phenolic compounds, among which the <strong>catechol<\/strong>, a recognized precursor of secondary organic aerosols. By day, sunlight drives most of the atmospheric oxidation. However, at night, another actor takes over, the <strong>nitrate radical<\/strong>, noted NO3.<\/p>\n<section class=\"incontent-related\"><span class=\"incontent-related__title\">Read also<\/span> <span class=\"incontent-related__desc\">A decay of one in ten billion detected at the LHCb detector, physicists knock on the door of the zeptoverse<\/span><\/section>\n<p>This radical forms when ozone reacts with nitrogen dioxide, two gases abundant in polluted plumes. By day, sunlight almost immediately destroys it, making it an exemplary <strong>nighttime oxidant<\/strong>. Thus, smoke that travels at night continues to transform, far from the fire that produced it.<\/p>\n<h2 class=\"wp-block-heading\">Md. Sohel Rana and Marcelo Guzman exposed thin films of catechol to relative humidity ranging from 0 to 90 %<\/h2>\n<p>The two chemists published their work in <strong>Environmental Science &amp; Technology<\/strong>. Their setup involved depositing <strong>thin layers<\/strong> of catechol, then exposing them to nitrate radicals generated from ozone and nitrogen dioxide. Additionally, the relative humidity varied from completely dry air to 90 %.<\/p>\n<p>To identify the products, the team combined Fourier-transform infrared spectroscopy, UV\u2013visible spectroscopy and several <strong>mass spectrometry<\/strong> techniques, including one coupled to ion chromatography. Consequently, the researchers could track both the formed molecules and their capacity to absorb light.<\/p>\n<section class=\"incontent-related\"><span class=\"incontent-related__title\">Read also<\/span> <span class=\"incontent-related__desc\">In Paris, sunset will come as early as December 11, 2026, but the darkest morning will not arrive until New Year<\/span><\/section>\n<h2 class=\"wp-block-heading\">In dry air, nitrocatechols form brown carbon, while humid air favors dicarboxylic acids<\/h2>\n<p>Under dry conditions, oxidation promotes nitration and the assembly of molecules. It yields mono-, di- and trinitrocatechols, accompanied by dimers and trimers of catechol. These products absorb strongly between 300 and 500 nanometers, a signature of <strong>brown carbon<\/strong> that traps part of the solar radiation.<\/p>\n<p>As humidity increases, the nitration capacity wanes. At the same time, the aromatic ring opens and yields <strong>dicarboxylic acids<\/strong>, including cis,cis-muconic acid, <em>2,3-dihydroxymalytic<\/em> acid and oxalic acid. Thus, the chemistry shifts from a functionalization logic to a fragmentation logic.<\/p>\n<h2 class=\"wp-block-heading\">This chemical shift could modify how models estimate the climate effect of wildfire plumes<\/h2>\n<p>Brown carbon locally warms the atmosphere by absorbing light, unlike many lighter aerosols. Consequently, smoke traversing a humid air mass could lose some of its <strong>light-absorbing molecules<\/strong> in favor of highly oxidized compounds. The authors emphasize that the water associated with aerosols governs the chemical and optical aging of these particles.<\/p>\n<section class=\"incontent-related\"><span class=\"incontent-related__title\">Read also<\/span> <span class=\"incontent-related__desc\">Centenarians and lifelong smokers unaffected intrigue the Atlas team, which tracks protective antibodies in their blood<\/span><\/section>\n<p>However, these measurements stem from laboratory experiments on a single model compound. They will need to be tested against real plumes, where hundreds of molecules react together. Yet, with the rise of megafires, incorporating nocturnal humidity into air-quality models now appears to be a logical step.<\/p>\n","protected":false},"excerpt":{"rendered":"","protected":false},"author":1,"featured_media":4177,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[2742,2741,1428,2740,2739,2738,1084,2736,2737,1326],"class_list":["post-4176","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news","tag-breaks","tag-brown","tag-continues","tag-determines","tag-evolve","tag-fires","tag-humidity","tag-nighttime","tag-smoke","tag-turns","generate-columns","tablet-grid-50","mobile-grid-100","grid-parent","grid-50"],"_links":{"self":[{"href":"https:\/\/www.farmersforum.ie\/trends\/wp-json\/wp\/v2\/posts\/4176","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.farmersforum.ie\/trends\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.farmersforum.ie\/trends\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.farmersforum.ie\/trends\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.farmersforum.ie\/trends\/wp-json\/wp\/v2\/comments?post=4176"}],"version-history":[{"count":1,"href":"https:\/\/www.farmersforum.ie\/trends\/wp-json\/wp\/v2\/posts\/4176\/revisions"}],"predecessor-version":[{"id":4178,"href":"https:\/\/www.farmersforum.ie\/trends\/wp-json\/wp\/v2\/posts\/4176\/revisions\/4178"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.farmersforum.ie\/trends\/wp-json\/wp\/v2\/media\/4177"}],"wp:attachment":[{"href":"https:\/\/www.farmersforum.ie\/trends\/wp-json\/wp\/v2\/media?parent=4176"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.farmersforum.ie\/trends\/wp-json\/wp\/v2\/categories?post=4176"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.farmersforum.ie\/trends\/wp-json\/wp\/v2\/tags?post=4176"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}