Growth rates of nucleation mode particles in Hyytiälä during 2003−2009: variation with particle size, season, data analysis method and ambient conditions

Abstract

Abstract. The condensational growth rate of aerosol particles formed in atmospheric new particle formation events is one of the most important factors influencing the lifetime of these particles and their ability to become climatically relevant. Diameter growth rates (GR) of nucleation mode particles were studied based on almost 7 yr of data measured during the years 2003-2009 at a boreal forest measurement station SMEAR II in Hyytiälä, Finland. The particle growth rates were estimated using particle size distributions measured with a Differential Mobility Particle Sizer (DMPS), a Balanced Scanning Mobility Analyzer (BSMA) and an Air Ion Spectrometer (AIS). Two GR analysis methods were tested. The particle growth rates were also compared to an extensive set of ambient meteorological parameters and trace gas concentrations to investigate the processes/constituents limiting the aerosol growth. The median growth rates of particles in the nucleation mode size ranges with diameters of 1.5-3 nm, 3-7 nm and 7-20 nm were 1.9 nm h −1 , 3.8 nm h −1 , and 4.3 nm h −1 , respectively. The median relative uncertainties in the growth rates due to the size distribution instrumentation in these size ranges were 25 %, 19 %, and 8 %, respectively. For the smallest particles (1.5-3 nm) the AIS data yielded on average higher growth rate values than the BSMA data, and higher growth rates were obtained from positively charged size distributions as compared with negatively charged particles. For particles larger than 3 nm in diameter no such systematic differences were found. For these particles the uncertainty in the growth rate related to Correspondence to: T. Yli-Juuti (taina.yli-juuti@helsinki.fi) the analysis method, with relative uncertainty of 16 %, was similar to that related to the instruments. The growth rates of 7-20 nm particles showed positive correlation with monoterpene concentrations and their oxidation rate by ozone. The oxidation rate by OH did not show a connection with GR. Our results indicate that the growth of nucleation mode particles in Hyytiälä is mainly limited by the concentrations of organic precursors.

Contribution of oxidized organic compounds to nanoparticle growth

“…In this case the particle growth rates as function of particle size was determined to be 2.2 nm h -1 , 2.8 nm h -1 and 3.2 nm h -1 in size ranges <3nm, 3-7 nm and 7-15 nm. The increased growth rate of the larger particles is similar to many observations of atmospheric particle growth rates [2].…”

“…Various volatile organic compounds (VOCs) are emitted by vegetation, and in the atmosphere these VOCs are oxidized mainly by ozone, OH and NO 3 into lower volatility compounds that are able to condense on particles. From long-term observations at a boreal forest station in Central Finland, it has been observed that particle growth rates are clearly highest at summertime at the same time as emissions of VOCs are also largest during the year [2].…”

Semi-empirical parameterization of size-dependent atmospheric nanoparticle growth in continental environments

“…Yli-Juuti et al (2011) also observed a correlation between monoterpene concentrations and 7-20 nm particle growth in the boreal forest site of Hyytiälä, Finland, indicating the importance of monoterpene oxidation products in the growth process. Also, a clear seasonal variation in the growth of 3-20 nm particles was observed in Hyytiälä, with highest values during the summer Hirsikko et al, 2005;Riipinen et al, 2011;Yli-Juuti et al, 2011). The growth of the smallest sub-3 nm particles in Hyytiälä, on the other hand, has not been observed to show such seasonality (Hirsikko et al, 2005;Yli-Juuti et al, 2011).…”

“…Several recent observations from different field sites suggest that the condensational growth rates of ambient nanoparticles increase with particle size (Hirsikko et al, 2005;Manninen et al, 2010;Yli-Juuti et al, 2011;Kuang et al, 2012). Yli-Juuti et al (2011) also observed a correlation between monoterpene concentrations and 7-20 nm particle growth in the boreal forest site of Hyytiälä, Finland, indicating the importance of monoterpene oxidation products in the growth process.…”

“…Therefore other compounds, e.g., organics or ammonia/amines, are expected to be important in the early growth of freshly nucleated particles (O'Dowd et al, 2002;Smith et al, 2005Smith et al, , 2008Pierce et al, 2011;Riipinen et al, 2012;Vehkamäki and Riipinen, 2012;Kulmala et al, 2013). Several recent studies point to the importance of organic compounds in growing atmospheric nanoparticles to climatically relevant sizes (e.g., Kuang et al, 2010;Yli-Juuti et al, 2011;Riipinen et al, 2012 and references therein), and capturing this organic contribution has been shown to be important for CCN predictions on regional scale .…”