Ozone and peroxyacetylnitrate in downtown Santiago, Chile

Peroxyacetylnitrate (PAN) and ozone have been measured during spring and early summer in downtown Santiago during 2002 and 2003. Although the values are lower than those reported at a site located downwind from the center of the city, ozone levels frequently surpass the air quality standard ( 80 ppb, 1 h or 60 ppb, 8 h mobile average), and PAN levels as high as 22 ppb have been measured. Ozone and PAN levels strongly correlate between them and with the maximum daily temperature. This dependence is not due to a direct relationship between temperature and irradiance, and allows a prediction of critical days from the temperature forecast. In fact, in days with temperatures below 29 °C, ozone quality standard is surpassed only 16% of the time, and PAN reaches values above 5 ppb only 7% of the measured days. On the other hand, when the temperature reaches above 29 °C, ozone surpass the quality standards 87% of the days and PAN values are above 5 ppb 83% of the measured days.