Texans love to say this, usually right after we’ve been griping about soggy lawns and muddy footprints on the carpet. “But, we sure do need this rain.”
And it’s true – we suffered through several years of drought, so it’s wonderful to see how green our countryside becomes with a little rain. Did you know that rain and other weather patterns can reduce the formation of ground-level ozone? Let’s review the ozone equation:
VOCs + NOx + Sunlight = Ozone
Volatile Organic Compounds plus Nitrogen Oxides, in the presence of Sunlight, results in the formation of ground-level ozone. This effect is most prominent on dry, hot, windless days, because the VOC and NOx precursors just float around in the air and react.
Windy days may dissipate emissions, but that’s a double-edged sword – it means that the precursors and ozone already in the air get blown over to the neighboring cities and counties. Rainy days usually mean a good amount of cloud cover, so we’ve taken Sunlight out of the equation. The precipitation reduces particulate matter pollution (dust, soot, and other fine particles) by washing it out of the air. Most importantly, since we know that dry weather increases ozone formation, that means the rain will help prevent ozone from forming. It just stands to reason that what everyone has been saying is true: