Increasing trends (2001–2018) in photochemical activity and secondary aerosols in Santiago, Chile
Camilo Menares, Laura Gallardo, Maria Kanakidou, Rodrigo Seguel, Nicolás Huneeus
Abstract
Despite the decline in partially (PM10) and fully (PM2.5) inhalable particles observed in recent decades, \nSantiago in Chile shows high levels of particle and ozone pollution. Attainment plans have emphasized \nmeasures aimed at curbing primary and, to some extent, secondary particles, but little attention has been \npaid to photochemical pollution. Nevertheless, ozone hourly mixing ratios in Eastern Santiago regularly \nexceed 110 ppbv in summer, and in winter maximum mixing ratios often reach 90 ppbv. Moreover, the sum \nof ozone and nitrogen dioxide shows an increasing trend of more than 3.5 ppbv per decade at 5 out of 8 \nstations. This trend is driven by increasing NO2, possibly associated with increasing motorization but also \nwith changes in photochemistry. To estimate the fraction of secondary particles in PM2.5 and due to the lack \nof long-term speciation data for particles, we use carbon monoxide as a proxy of primary particles and ozone \ndaily maxima as a proxy for secondary particle formation. We find a growing fraction of secondary particles \ndue to an increase in the oxidizing capacity of Santiago’s atmosphere. This stresses the need for new curbing \nmeasures to tackle photochemical pollution. This is particularly needed in the context of a changing climate.