What the COVID-19 lockdown revealed about photochemistry and ozone production in Quito, Ecuador

The COVID-19 lockdown in Quito, Ecuador, revealed a significant shift in the photochemical regime of ozone production. Despite dramatic drops in primary precursors like NO and CO due to mobility restrictions, ambient ozone levels remained unchanged. Using a chemical box model constrained by observations of ozone, NOx, CO, and meteorology—along with VOC/CO ratios from Mexico City—a study found that reduced NOx during morning rush hours increased ozone production rates by more than 100%, reaching up to 23 ppbv h−1. Further analysis, simulating post-lockdown conditions while maintaining pre-lockdown VOC levels, tripled ozone production in mid-morning and sustained elevated rates throughout the day. These findings highlight the complex interplay between NOx reductions and VOCs in urban photochemistry, offering insights into potential scenarios for ozone accumulation.

Cazorla, M., Herrera, E., Palomeque, E., & Saud, N. (2021). What the COVID-19 lockdown revealed about photochemistry and ozone production in Quito, Ecuador. Atmospheric Pollution Research, 12(1), 124–133. https://doi.org/10.1016/j.apr.2020.08.028