Effects of Oceanic Emissions of Halocarbons on the Air Quality of Chilean Coastal Urban Zones

Abstract Description: Oceans are the largest sources of biogenic emissions in the atmosphere. In this context, halocarbons are generated from biological processes and exchanged with the air. These species have been studied in recent years because of their relation to the Earth's climate system by the products obtained from photolysis and reaction pathways with atmospheric oxidants.

Unfortunately, no regional modeling studies have used CMAQ, where oceanic halocarbon emissions are included to assess atmospheric oxidation and air pollution at the surface level in Chile. According to environmental authorities, five urban coastal zones in Chile are exposed to a mix of anthropogenically polluted air masses and cleaner marine sea breezes. This phenomenon is usually reported in coastal areas, indicating strong interaction between oceans and land, resulting in a diverse aerosol population with a high degree of external mixing.

This study aimed to evaluate the effect of marine halocarbon emissions on air quality in the coastal zones of Chile. This research study was developed using the WRF-SMOKE-CMAQ model system. The period of analysis was April-May and July-August 2019, starting on April/July 1st considering 10 days as a spin-up.

The evaluation of the effects of halocarbons on sulfur dioxide (SO2) and ozone (O3) assumes a scenario with emissions from the ocean of those compounds and others with zero emissions. As a result, a positive contribution of halocarbons to the production of SO2 in the air was obtained. However, the average effect of halocarbons on SO2 concentrations in all study cities was less than 1 %. In contrast, the negative contribution obtained for O3 revealed the destruction of this pollutant due to the production of halogen radicals by the decomposition of halocarbons in the air, confirming the literature. In addition, O3 had a marked impact on the analysis period. During winter, the effect of the mean hourly concentration decreased. This could be related to a decrease in the photolysis reaction rate owing to the reduction in solar radiation during this period. Future studies must be conducted in the summer period, when higher emissions of halocarbons are present in the Southern Hemisphere.