Browsing by Subject "CONDENSATION NUCLEI"

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  • Baranizadeh, Elham; Nieminen, Tuomo; Yli-Juuti, Taina; Kulmala, Markku; Petäjä, Tuukka; Leskinen, Ari; Komppula, Mika; Laaksonen, Ari; Lehtinen, Kari E. J. (2017)
    The formation rates of 3 nm particles were estimated at SMEAR IV, Puijo (Finland), where the continuous measurements extend only down to 7 nm in diameter. We extrapolated the formation rates at 7 nm (J(7)) down to 3 nm (J(3)) based on an approximate solution to the aerosol general dynamic equation, assuming a constant condensational growth rate, a power-law size-dependent scavenging rate, and negligible self-coagulation rate for the nucleation mode particles. To evaluate our method, we first applied it to new particle formation (NPF) events in Hyytiala (Finland), which extend down to 3 nm, and, therefore, J(3) and J(7) can be determined directly from the measured size distribution evolution. The Hyytiala results show that the estimated daily mean J(3) values slightly overestimate the observed mean J(3), but a promising 91% of the estimated J(3) values are within a factor of 2 from the measured ones. However, when considering detailed daily time evolution, the agreement is not as good due to fluctuations in data as well as uncertainties in estimated growth rates, which are required in order to calculate the time lag between formation of 3 and 7 nm particles. At Puijo, the mean J(7) for clear NPF days during April 2007-December 2015 was 0.44 cm(-3) s(-1), while the extrapolated mean J(3) was 0.61 cm(-3) s(-1).
  • Wehner, B.; Werner, F.; Ditas, F.; Shaw, R. A.; Kulmala, M.; Siebert, H. (2015)
    During the CARRIBA (Cloud, Aerosol, Radiation and tuRbulence in the trade wInd regime over BArba-dos) campaign, the interaction between aerosol particles and cloud microphysical properties was investigated in detail, which also includes the influence of clouds on the aerosol formation. During two intensive campaigns in 2010 and 2011, helicopter-borne measurement flights were performed to investigate the thermodynamic, turbulent, microphysical, and radiative properties of trade-wind cumuli over Barbados. During these flights, 91 cases with increased aerosol particle number concentrations near clouds were detected. The majority of these cases are also correlated with enhanced irradiance in the ultraviolet (UV) spectral wavelength range. This enhancement reaches values up to a factor of 3.3 greater compared to background values. Thus, cloud boundaries provide a perfect environment for the production of precursor gases for new particle formation. Another feature of cloud edges is an increased turbulence, which may also enhance nucleation and particle growth. The observed events have a mean length of 100 m, corresponding to a lifetime of less than 300 s. This implies that particles with diameters of at least 7 nm grew several nanometers per minute, which corresponds to the upper end of values in the literature (Kulmala et al., 2004). Such high values cannot be explained by sulfuric acid alone; thus extremely low volatility organic compounds (ELVOCs) are probably involved here.