Case Study: Global Troposhperic Ozone Production - NARE
In the 1990s, CSD (formerly Aeronomy Laboratory) participated in a major international field and modeling campaign that has shown that human-made chemicals are responsible for the generation of ozone in the troposphere over the North Atlantic Ocean. The research addresses the growing concern that ozone and its precursors (the "starting ingredients," volatile organic compounds (VOCs) and nitrogen oxides) are transported from the North American continent and can influence ozone on a hemispheric scale, where it acts as one of the gases that could perturb the Earth's radiation budget.
The effort was part of the North Atlantic Regional Experiment (NARE), an activity of the International Global Atmospheric Chemistry Project (IGAC). In field intensives starting in 1991, comprehensive chemical and dynamical measurements have been made from several airborne platforms and from various ground-based stations along the Atlantic Seaboard and spanning the northern Atlantic Ocean. The measurements tracked the changing composition of air masses containing pollutants from eastern North America as these air masses were carried across the North Atlantic. By measuring carbon monoxide, ozone, and other trace gases, the researchers have shown that the "seeds" of the summertime ozone are the human-made precursors emitted from the heavily populated regions of the North American Continent.
Members of the Tropospheric Chemistry and Theoretical Aeronomy Projects of CSD have played leading roles not only in the field and modeling components of NARE, but also in its design and organization.
Evidence of Anthropogenic Ozone Production and Export. Measurements of ozone and carbon monoxide (CO) at three sites in the North Atlantic have shown that summertime ozone is produced from human emissions of "precursor" (ingredient) gases from the North American continent. Carbon monoxide is an anthropogenic pollutant that is relatively unreactive (lifetime: about 1 month in the summer) and can be used as a "tracer" of human-made pollution. The measured relations between the concentrations of O3 and CO in the air carried over the North Atlantic, coupled with the inventoried emissions of CO in eastern North America, leads to the estimate that approximately 10 billion pounds of ozone are exported per summer from the North American continent. This amount is greater than that reaching the lower troposphere in this region from the stratosphere, which is the primary natural source of ozone.