Abstract
ABSTRACT Despite reduction efforts, the concentration of PM2.5 (particulate matter ≤ 2.5 µm in diameter) has remained steady or even grown slightly in Santiago, Chile, over the last few years. However, this potential increase may be due to the formation of secondary particles rather than a rise in primary emissions. Therefore, this study measured the size distribution of particulate matter with an Electrical Low Pressure Impactor (ELPI; Dekati) to investigate the generation of secondary ultrafine particles at several sites in this metropolitan area during 2013 and 2018. Little formation was detected during winter, but more activity was observed during fall, and the highest generation of these particles was found during summer, when the number of new particles between 10 and 20 nm in diameter displayed an obvious peak in the afternoon during periods of high solar radiation. Overall, no clear relationship was discerned between the secondary particle number and the UV radiation until the latter exceeded ~4.5 kJ m–2, when an almost linear correlation (R2 = 0.739) appeared. Additionally, the particle number exhibited a much lower correlation with the total solar energy, indicating that UV solar radiation plays the major role in ultrafine particle formation. However, these trends may only apply to polluted cities, which already contain elevated particulate matter concentrations. Also, the fact that secondary formation primarily occurs in Santiago during summer, when the PM2.5 level is low, confirms that large numbers of pre-existing particles inhibit the creation of new ones.
Highlights
The city of Santiago, Chile, is known to have very high PM2.5 and PM10 concentrations, especially during winter (Artaxo et al, 1999; Kavouras et al, 2001; Gramsch et al, 2006)
To study if there is a relationship between solar energy and new ultrafine particle formation, a correlation plot has been calculated between these variables for all the data
Evidence of new particle formation was noted at several sites in Santiago, Chile, on days with high solar radiation, mostly during summer
Summary
The city of Santiago, Chile, is known to have very high PM2.5 and PM10 concentrations, especially during winter (Artaxo et al, 1999; Kavouras et al, 2001; Gramsch et al, 2006). The ELPI was used to measure particle number at several urban background and curbside sites in Santiago. New Particle Formation and Radiation NPF events have been observed at several places and years, mostly on days with high solar irradiance and clean environments (Dunn et al, 2004; Kulmala et al, 2004; Sorribas et al, 2015).
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