Fig. 1.
Topographic features affecting Santiago and location of air quality monitoring stations. Also shown is the site (x, San Joaquín) where aerosol speciation was assessed in 2013 by Villalobos et al. (2015). The map on the left (a) shows the location of the city and the topography of the area. The map on the right (b) shows a close-up of the map and the location of the stations in the air quality network of Santiago. Stations are: F (Independencia); L (La Florida); M (Las Condes); N (Parque O’Higgins); O (Pudahuel); P (Cerrillos); Q (El Bosque); R (Cerro Navia); S (Puente Alto); T (Talagante). For instrumentation in the air quality network and other details see Table S1.
Fig. 2.
Relationship between daily averages of PM2.5 (in µg/m3) and CO (in ppmv) for Las Condes station in Eastern Santiago, between 2001 and 2018. Data are stratified according to season: warm (September through February), shown in the left panel, and cold (March through August) shown in the right panel. Data are also stratified according to ozone daily maximum range: horizontal panels show the relation for low (a,b), medium (c,d), medium-to-high (e,f), and high (g,h) photochemical activity. The corresponding linear regression lines (shown in black) and correlation factors are also shown, as well as the number of concurrent CO and PM2.5 measurements (n). The percentage is calculated as the ratio between the cold/warm season points with respect to the total number of data points considered in the regression.
Fig. 3.
Background oxidant, i.e., Ox=O3+NO2, mixing ratios for Pudahuel and Las Condes for the period 2005–2018 when both O3, NO and NO2 are available. The upper panels show the daylight hours Ox vs NOx linear regressions according to Neri et al. (1989) for the cold (blue) and warm (brown) seasons, in Las Condes (left) and Pudahuel (right). The lower panel shows the evolution of the intercept of the linear regressions of each year between 2005 and 2018, for Las Condes (black symbols) and for Pudahuel (grey symbols).
Fig. 4.
Evolution of the daily (24 hours) secondary aerosol fraction (in %) as calculated by the methodology by Chang and Lee (2007). The upper (lower) panel shows the results (bars) for Las Condes (Pudahuel) station in Eastern (Western) Santiago, considering O3, max > 45 ppbv. The error range is calculated as the standard deviation of each 2-year average. Results are shown for the whole year (black bars) as well as for the cold (green) and warm (red) seasons.
Table 1.
Trends and trend error estimates of O3, NO2, Ox, and PM2.5 observed at Eastern (Las Condes) and Western (Pudahuel) Santiago monitoring stations for different periods, based on monthly mean observations. Data source: http://sinca.mma.gob.cl/. Time series are shown in the supplementary material (Figs. S5 and S6a–f for Las Condes and Pudahuel respectively).
Fig. 5.
Average fraction of secondary aerosol (in %) and standard deviation segregated by daily ozone maximum range, and by period, for stations Las Condes (Left panel) and Pudahuel (Right panel). The different time periods considered, i.e., 2001–2008 and 2009–2018, are shown in black and grey, respectively.
Fig. 6.
Diurnal cycle of secondary aerosol fraction (in %) estimated at Las Condes station for the warm season (September–February) for the period 2001–2018. Data are presented as box plots: the central mark in the box indicates the median of the distribution, the edges of the box are the 25th and 75th percentiles, the whiskers extend to the most extreme data points not considered outliers, and outliers are plotted individually (red crosses). The number of outliers is less than 2% of the points considered in each box. See details in the text.
Fig. 7.
Monthly averaged secondary fraction of PM2.5 (black dotted line) for stations Las Condes (upper panel) and La Florida (lower panel) in Eastern Santiago as estimated using the empirical method (Chang and Lee, 2007). The grey colour indicates the standard deviation of the monthly values calculated over daily averages. The corresponding monthly averaged measured by Villalobos et al. (2015) at San Joaquín near La Florida station are also shown (blue dashed line).
Fig. 8.
Decadal trends (%) in O3, NO2 and Ox=O3+NO2 in Santiago for the period 2009–2018. Blurry circles with an asterisk indicate statistically non-significant trends. Trends are calculated over deseasonalized monthly averaged values using the approach by Duncan et al. (2016).
Table 2.
Chemical composition of aerosols as measured in Santiago in previous studies. Secondary inorganic (SIA) and organic (SOA) aerosol components are indicated when available. N/A indicates not available. The percentage corresponds to the fraction of total aerosol. We also include our estimate of the secondary fraction (%) and the total PM2.5 mass concentration (calculated as hourly averages over the period) at the closest station.