Oh Zone

New Research on Ozone’s Impact on Tropical Forests
A study published in Nature Geoscience in September 2024, titled Reduced productivity and carbon drawdown of tropical forests from ground-level ozone exposure, highlights the extensive damage caused by tropospheric ozone. The research shows that elevated ground-level ozone — primarily generated by human activity — severely diminishes plant productivity and reduces the ability of forests to absorb carbon. Unfortunately, trimming back dead parts of a tree won’t extend its longevity, as the damage from ozone is systemic and affects the tree’s overall health.

The researchers experimentally measured the ozone susceptibility of various tropical tree species and incorporated this data into a dynamic global vegetation model. Their findings are alarming: they estimate that human-derived ozone causes a substantial decline in net primary productivity (NPP) across all tropical forests, with regions like Asia experiencing losses of up to 10.9%. This reduction in productivity translates into a cumulative loss of 0.29 petagrams of carbon (PgC) per year, equating to roughly 17% of the tropical land carbon sink since 2000. Ozone, therefore, not only harms human health but also disrupts critical natural processes that help mitigate climate change by removing carbon dioxide from the atmosphere.

Ozone and the Biofuel Paradox: Ethanol’s Role in Pollution
One of the more troubling contributors to tropospheric ozone is the increased use of ethanol in gasoline. Over the past few years, ethanol has become a mandated additive to gasoline blends, touted as a cleaner alternative to traditional fossil fuels. For example, in Pennsylvania, a 10% ethanol blend in gasoline and a 30% ethanol blend in diesel fuel are required to reduce harmful emissions. However, this practice has resulted in unintended consequences — specifically, the creation of more ozone.

As early as 1999, scientists and environmentalists began questioning ethanol’s role in ozone creation. A report by David Morris and Jack Brondum of the Institute for Local Self-Reliance in 2000 acknowledged ethanol’s benefits but also raised concerns. “Ethanol is an attractive fuel with many undisputed environmental and economic development benefits. Yet it suffers from one disadvantage: it raises the volatility of gasoline.”

This increased volatility leads to greater emissions of hydrocarbons, which in turn form more ozone when exposed to sunlight. Environmentalists feared that increased hydrocarbon emissions would lead to heightened ozone levels and pose a serious public health risk.

Despite these concerns, ethanol received widespread support from those advocating for biofuels, and it was exempted from certain clean air emissions standards. In 1994, California engaged in a legal battle with the EPA over ethanol’s contribution to ozone pollution. EPA spokesman John Millett noted that if ethanol was shown to exacerbate air quality issues, a waiver could be granted, but the evidence was still being carefully analyzed.