John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Scientists working in smoggy Houston say planting a 1.5-square-mile forest would make the air more breathable.
Ozone is corrosive to the life it touches, bringing misery to straining lungs and withering millions of tons of crops every year. And with the atmosphere growing warmer and warmer, bouts of extreme ozone pollution are expected to become more frequent and noxious.
What can humanity do to fight this pollutant, which contributes to about 152,000 premature deaths worldwide every year? Scientists working in the highly polluted area around metro Houston believe they've found an answer, and it is, Plant a bunch of trees.
Granted, some types of trees like black gum and poplar can lead to the production of more ozone, thanks to the high levels of volatile organic compounds they emit. But studies have shown that certain urban area-adjacent forest makeups—notably, ones in Madrid and near Mexico City—absorb enough chemicals compared to what they put out that they can improve local air quality. This is the kind of beneficial vegetation that interests Timm Kroeger, a researcher at the Nature Conservancy and lead author of a new study examining the hypothetical impact of a new, 1.5-square-mile forest on the outskirts of Houston.
Tactics to fight ozone pollution nowadays take the form of reducing fossil-fuel emissions via factory retrofits, partial plant shutdowns, switching to different fuels, and other such engineering schemes. Kroeger and his colleagues think strategic reforestation of near-urban areas could be an efficient and cost-effective supplement to these measures. Using weather data and computer models, they simulated a freshly grown forest in the Houston-Galveston-Brazoria nonattainment area, a dingy-skied region that Texas says has a "severe" ozone problem. Over the course of 30 years, they say this green space could remove as much as 310 tons of ozone from the atmosphere, an estimate they call "conservative."
So where would the land come from to support this cleansing forest? The researchers suggest Houston stakeholders could buy agricultural plots, an expense they say would be outmatched by the project's social value as a long-term carbon sink—such a forest would help mitigate the "sum of future damages from increased atmospheric CO2 concentrations," they claim. And they have another, quite Texas-sounding idea to make the project financially sound. From the study:
The competitiveness of reforestation projects may also be enhanced by interplanting of fast-growing species such as Populus deltoides in our study area to support a one-time selective timber harvest. The impact of such harvests on the cost per ton of [ozone precursors] reduced depends on timber prices, volume harvested, accessibility, distance to the nearest mill, and requirements of the relevant [carbon] offset protocols.
Selective reforestation could be a viable option for many parts of the planet struggling with ozone pollution, according to Kroeger and company. They've even plotted a map indicating where they believe it could help in the U.S. It looks like their plan would make the drive on I-95 from D.C. to New York a ton more scenic: