New car smell, forest haze and bitter coffee share one chemical family
That pleasant new car smell is a cloud of volatile organic compounds, chemicals that evaporate readily at room temperature. People release plenty of them from paint, fuel and aerosols, yet plants emit far more, and a forest the size of Pennsylvania can breathe out millions of kilograms of them on a single summer day.
What makes these compounds volatile is a high vapour pressure, which goes hand in hand with a low boiling point, so many of their molecules escape into the surrounding air. Definitions vary by regulator. Health Canada focuses on organic compounds boiling between roughly 50 and 250 °C, the European Union sets a vapour pressure threshold, and California's air board prefers the term reactive organic gases. American smog rules even exempt compounds judged barely reactive, which can mislead when thinking about indoor air.
Nature is the biggest source. Excluding methane, living things release an estimated 760 teragrams of carbon a year as these compounds, mostly from plant leaves and especially as isoprene. They serve as signals, luring pollinators, deterring herbivores and passing messages between plants. A forest of 62,000 square kilometres gives off about 3.4 million kilograms of terpenes on a typical August day. Bitter flavours in olives, coffee and dark chocolate come from taste receptors detecting such molecules.
Human activity contributes around 142 teragrams of carbon annually. Fossil fuels are a major source, with ethane the most common compound. Roughly 12 billion litres of paint are made each year, and the industry is moving toward water-based solvents, while aerosol propellants like butane and propane add about 1.3 million tonnes. Biofuels and burning rain forests contribute too.
Indoors, concentrations are consistently higher than outside, sometimes by a factor of ten, because thousands of products release them: varnishes, cleaners, printers, glues, permanent markers and furnishings. Cooking and cleaning add more, and once airborne some react with ozone to form others such as formaldehyde. New buildings are especially heavy emitters as fresh materials off-gas. Most of these compounds are not acutely toxic, though some may carry long-term health effects, which is why indoor use is often regulated.
Source: Volatile organic compound
