Variability of particulate matter (PM10) in Santiago, Chile by phase of the Madden–Julian Oscillation (MJO)

Abstract Topographical, economical, and meteorological characteristics of Santiago, Chile regularly lead to dangerously high concentrations of particulate matter (PM 10 ) in the city during winter months. Although the city has suffered from poor air quality for at least the past forty years, variability of PM 10 in Santiago on the intraseasonal time scale had not been examined prior to this study. The Madden–Julian Oscillation (MJO), the leading mode of atmospheric intraseasonal variability, modulates precipitation and circulation on a regional and global scale, including in central Chile. In this study, surface PM 10 concentrations were found to vary by phase of the MJO. High PM 10 concentrations occurred during phases 4, 5 and 7, and low concentrations of PM 10 occurred during phases 1 and 2. Precipitation, low-troposphere circulation, and lower-troposphere temperatures supported the observed PM 10 variability. For example, during phases 1 and 2 (low PM 10 ), precipitation was above normal, morning and evening temperature inversions were less intense than normal, and 900 hPa winds were anomalously westerly. During phases 4, 5 and 7 (high PM 10 ), precipitation was normal to below normal, morning and evening temperature inversions were stronger than normal, and 900 hPa winds were anomalously easterly.