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The effect of ammonia and acids on cloud droplet formation
Pergamon
J. Aerosol Sci. Vol. 28, Suppl. 1, pp. $419-$420, 1997
PH:S0021-8502(97)00256-5
©1997 Elsevier Science Ltd. All rights reserved Printed in C,-raatBritain 0021-8502/97 $17.00+0.00
The effect of ammonia and acids on cloud droplet formation Markku Kulmala, Timo Mattila and Anne Toivonen University of Helsinki, Department of Physics P. O. Box 9, FIN-00014 University of Helsinki, Finland Keywords Multicomponent condensation, cloud droplet activation, acids, ammonia The effects of the availability of condensable material (other than water) in the gas phase on cloud droplet formation and on the radiative properties of clouds have been studied using an adiabatic air parcel model with detailed multicomponent condensation (Kulmala et al., 1993, 1996; Mattila 1996). In the simulations water, ammonia, nitric acid, hydrochloric acid and sulphuric acid are condensing simultaneously. The pre-existing lognormal particle distribution used is bimodal in size and also bimodal in hygroscopicity. The first distribution consists of less hygroscopic Aitken mode particles, the second of more hygroscopic Aitken mode particles, the third of less hygroscopic accumulation mode particles and the fourth of more hygroscopic accumulation mode particles. Particles are chosen to be partly some insoluble substance and partly hygroscopic salt (ammonium sulphate). In Table 1 results of model calculations are presented when initial aerosol particle concentrations were 150 and 300/cc. The more hygroscopic accumulation-mode particles play the most significant role in the cloud droplet formation process. The more hygroscopic Aitken mode particles play a significant role as well as less hygroscopic accumulation mode particles if acid and ammonia concentrations are high. Activated fractions are higher when initial particle concentration is low. The hygroscopic bimodality changes the common picture of activation. If we have uniform hygroscopicity, only particles belonging to accumulation mode are able to form cloud droplets. In the case of bimodal hygroscopicity also a significant fraction of Aitken mode particles will form cloud droplets. According to our simulations the sum of different trace gas concentrations seems to be the driving force for the enhancement of droplet formation. Ammonia increase the effect of acids significantly. Since we can sum up concentrations of different acids, and ammonia will help activation, multicomponent droplet formation increase the droplet concentration more than the droplet formation by binary condensation (water + nitric acid). The hygroscopicity of pre-existing aerosol particles and concentrations of condensable gases can influence the optical thickness and reflectance of clouds. The change in optical
$419
$420
HNOa+HCL (ppb)
Abstractsof the 1997EuropeanAerosolConference
NH~ Total (A) Frac. of drop. (A) Total (B) Frac. of drop. (B) (ppb) (cm -z) (cm -a)
0.1 0.1 39.73 0.2649 66.06 0.2202 1 0.1 58.02 0.3868 88.31 0.2944 10 0.1 96.64 0.6443 134.63 0.4488 0.1 1 52.93 0.3528 81.09 0.2703 1 1 142.17 225.52 0.9478 0.7517 10 1 148.68 0.9912 297.36 0.9912 94.45 0.1 10 78.84 0.5256 0.3148 1 10 148.68 0.9912 293.06 0.9769 10 10 148.68 0.9912 297.36 0.9912 TABLE 1: Modes 1 and 2 belong to Aitken mode (less hygroscopic and more hygroscopic), modes 3 and 4 belong to accumulation mode (less hygroscopic and more hygroscopic). (A) refers to number concentration of 100 (60+40) in Aitken mode and 50 (15+35) in accumulation mode. (B) refers to number concentration of 200 (120+80) in Aitken mode and 100 (30+70) in accumulation mode. The initial mean radius was 30 nm in Aitken mode and 100 nm in accumulation mode. The initial soluble salt mass fraction in the less hygroscopic modes (1 and 3) was 0.05 and in the more hygroscopic modes (2 and 4) was 0.5. The standard deviation was 1.35 in Aitken mode and 1.6 in accumulation mode. The initial temperature was 20°C, initial pressure was 1000 mbar and updraft velocity was 0.1
m/$. thickness (r) vary as a function of number concentration of pre-existing particles. The values of Ar/T are very high even over 1.0, when multicomponent condensation of acids and ammonia has been taken into account. A r / r is significantly lower if only binary condensation (nitric acid + water) is considered (see Kulmala et al., 1996).
References Kulmala M., Laaksonen, A., Korhonen, P., Vesala, T., Ahonen, T., Barrett, J. C., (1993), J. Geophys. Res. 98, 22949-22958. Kulmala, M., Korhonen, P., Vesala, T., Hansson, H.-C., Noone, K., Svenningsson, B., (1996), Tellus 48B, 347-360. Mattila, T., (1996), M.Sc. Thesis, University of Helsinki, Department of Physics.
J. Aerosol Sci. Vol. 28, Suppl. 1, pp. $419-$420, 1997
PH:S0021-8502(97)00256-5
©1997 Elsevier Science Ltd. All rights reserved Printed in C,-raatBritain 0021-8502/97 $17.00+0.00
The effect of ammonia and acids on cloud droplet formation Markku Kulmala, Timo Mattila and Anne Toivonen University of Helsinki, Department of Physics P. O. Box 9, FIN-00014 University of Helsinki, Finland Keywords Multicomponent condensation, cloud droplet activation, acids, ammonia The effects of the availability of condensable material (other than water) in the gas phase on cloud droplet formation and on the radiative properties of clouds have been studied using an adiabatic air parcel model with detailed multicomponent condensation (Kulmala et al., 1993, 1996; Mattila 1996). In the simulations water, ammonia, nitric acid, hydrochloric acid and sulphuric acid are condensing simultaneously. The pre-existing lognormal particle distribution used is bimodal in size and also bimodal in hygroscopicity. The first distribution consists of less hygroscopic Aitken mode particles, the second of more hygroscopic Aitken mode particles, the third of less hygroscopic accumulation mode particles and the fourth of more hygroscopic accumulation mode particles. Particles are chosen to be partly some insoluble substance and partly hygroscopic salt (ammonium sulphate). In Table 1 results of model calculations are presented when initial aerosol particle concentrations were 150 and 300/cc. The more hygroscopic accumulation-mode particles play the most significant role in the cloud droplet formation process. The more hygroscopic Aitken mode particles play a significant role as well as less hygroscopic accumulation mode particles if acid and ammonia concentrations are high. Activated fractions are higher when initial particle concentration is low. The hygroscopic bimodality changes the common picture of activation. If we have uniform hygroscopicity, only particles belonging to accumulation mode are able to form cloud droplets. In the case of bimodal hygroscopicity also a significant fraction of Aitken mode particles will form cloud droplets. According to our simulations the sum of different trace gas concentrations seems to be the driving force for the enhancement of droplet formation. Ammonia increase the effect of acids significantly. Since we can sum up concentrations of different acids, and ammonia will help activation, multicomponent droplet formation increase the droplet concentration more than the droplet formation by binary condensation (water + nitric acid). The hygroscopicity of pre-existing aerosol particles and concentrations of condensable gases can influence the optical thickness and reflectance of clouds. The change in optical
$419
$420
HNOa+HCL (ppb)
Abstractsof the 1997EuropeanAerosolConference
NH~ Total (A) Frac. of drop. (A) Total (B) Frac. of drop. (B) (ppb) (cm -z) (cm -a)
0.1 0.1 39.73 0.2649 66.06 0.2202 1 0.1 58.02 0.3868 88.31 0.2944 10 0.1 96.64 0.6443 134.63 0.4488 0.1 1 52.93 0.3528 81.09 0.2703 1 1 142.17 225.52 0.9478 0.7517 10 1 148.68 0.9912 297.36 0.9912 94.45 0.1 10 78.84 0.5256 0.3148 1 10 148.68 0.9912 293.06 0.9769 10 10 148.68 0.9912 297.36 0.9912 TABLE 1: Modes 1 and 2 belong to Aitken mode (less hygroscopic and more hygroscopic), modes 3 and 4 belong to accumulation mode (less hygroscopic and more hygroscopic). (A) refers to number concentration of 100 (60+40) in Aitken mode and 50 (15+35) in accumulation mode. (B) refers to number concentration of 200 (120+80) in Aitken mode and 100 (30+70) in accumulation mode. The initial mean radius was 30 nm in Aitken mode and 100 nm in accumulation mode. The initial soluble salt mass fraction in the less hygroscopic modes (1 and 3) was 0.05 and in the more hygroscopic modes (2 and 4) was 0.5. The standard deviation was 1.35 in Aitken mode and 1.6 in accumulation mode. The initial temperature was 20°C, initial pressure was 1000 mbar and updraft velocity was 0.1
m/$. thickness (r) vary as a function of number concentration of pre-existing particles. The values of Ar/T are very high even over 1.0, when multicomponent condensation of acids and ammonia has been taken into account. A r / r is significantly lower if only binary condensation (nitric acid + water) is considered (see Kulmala et al., 1996).
References Kulmala M., Laaksonen, A., Korhonen, P., Vesala, T., Ahonen, T., Barrett, J. C., (1993), J. Geophys. Res. 98, 22949-22958. Kulmala, M., Korhonen, P., Vesala, T., Hansson, H.-C., Noone, K., Svenningsson, B., (1996), Tellus 48B, 347-360. Mattila, T., (1996), M.Sc. Thesis, University of Helsinki, Department of Physics.