Abstract
Abstract. The capability to accurately yet efficiently represent atmospheric nanoparticle growth by biogenic and anthropogenic secondary organics is a challenge for current atmospheric large-scale models. It is, however, crucial to predict nanoparticle growth accurately in order to reliably estimate the atmospheric cloud condensation nuclei (CCN) concentrations. In this work we introduce a simple semi-empirical parameterization for sub-20 nm particle growth that distributes secondary organics to the nanoparticles according to their size and is therefore able to reproduce particle growth observed in the atmosphere. The parameterization includes particle growth by sulfuric acid, secondary organics from monoterpene oxidation (SORGMT) and an additional condensable vapor of non-monoterpene organics ("background"). The performance of the proposed parameterization was investigated using ambient data on particle growth rates in three diameter ranges (1.5–3 nm, 3–7 nm and 7–20 nm). The growth rate data were acquired from particle/air ion number size distribution measurements at six continental sites over Europe. The longest time series of 7 yr (2003–2009) was obtained from a boreal forest site in Hyytiälä, Finland, while about one year of data (2008–2009) was used for the other stations. The extensive ambient measurements made it possible to test how well the parameterization captures the seasonal cycle observed in sub-20 nm particle growth and to determine the weighing factors for distributing the SORGMT for different sized particles as well as the background mass flux (concentration). Besides the monoterpene oxidation products, background organics with a concentration comparable to SORGMT, around 6 × 107 cm−3 (consistent with an additional global SOA yield of 100 Tg yr−1) was needed to reproduce the observed nanoparticle growth. Simulations with global models suggest that the "background" could be linked to secondary biogenic organics that are formed in the presence of anthropogenic pollution.
Highlights
Earth System Sciences eterization was investigated using ambient data on particle growth rates in three diameter ranges (1.5–3 nm, 3–7 nm and 7–20 nm)
+kbg dp × ISORG,bg dp, where ISA is the mass flux caused by sulfuric acid, ISORG,MT is the maximum mass flux by monoterpene first-order oxidation products, and ISORG,bg is the mass flux from other condensable compounds, presumably organics that have not originated from monoterpene oxidation and do not have a seasonal dependence. kMT(dp) and kbg(dp) are weighing factors describing the fractions of ISORG,MT and ISORG,bg that condense onto nanoparticles having diameter dp, and have values between 0 and 1
The highest sulfuric acid concentrations were observed during springtime, and in general the concentrations of sulfuric acid were lower than those of secondary organics from monoterpene oxidation (SORGMT)
Summary
Earth System Sciences eterization was investigated using ambient data on particle growth rates in three diameter ranges (1.5–3 nm, 3–7 nm and 7–20 nm). The growth rate data were acquired from particle / air ion number size distribution measurements at six continental sites over Europe. The extensive ambient measurements made it possible to test how well the parameterization captures the seasonal cycle observed in sub nm particle growth and to determine the weighing fac-. Atmospheric aerosol particles affect our life multiple ways. Large aerosol particles with dry diameters of around. 70 nm (Dusek et al, 2006) can act as cloud condensation nuclei (CCN) and form cloSudodlirdoplEetas.rCthloud properties are affected by the composition and concentration of CCN (Rosenfeld et al, 2008) whereas the concentration of CCN
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