Determination of the Origin of High Tropospheric Ozone Levels in the Central Andes Mountains of Chile Using CMAQ

High tropospheric ozone levels have been recorded in the Central Andes Mountains of Chile. This region is predominantly rural and lacks significant local sources of ozone precursors. This study aims to determine the origin of these elevated ozone levels using the Community Multiscale Air Quality (CMAQ) modeling system.

The CMAQ model was driven by emissions from point, area, on-road, nonroad, and biogenic sources. It was processed using the SMOKE model, and meteorological conditions were simulated with the WRF model. Model performance was validated against hourly ozone observations, and the Integrated Source Apportionment Method (ISAM) was applied to determine the contribution of different sources to ozone formation.

Results indicate that ozone in the Metropolitan Region is primarily formed from on-road and nonroad mobile sources, while in Los Andes and Portillo, high ozone levels result from the transport of aged ozone from urban areas. The low NOx/NOy ratios observed in these mountainous regions confirm the presence of aged air masses, indicating that ozone is not generated locally but rather accumulated through long-range transport. Ozone formation in the Metropolitan Region is VOC-limited, meaning that reducing VOC emissions would lower both local ozone concentrations and transported ozone in rural and mountainous areas.

Additionally, areas in the Andes Mountains were identified with even higher ozone concentrations than currently monitored, emphasizing the need to expand the air quality monitoring network. Given the impact of ozone on sensitive high-altitude ecosystems, we recommend implementing a secondary air quality standard in Chile, as the current framework includes only a primary standard.

This study comprehensively analyzes ozone behavior in complex terrain and lays the foundation for targeted mitigation strategies to protect public health and ecosystems in central Chile.