P. H. McMurry

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Publications (3)0 Total impact

  • Article: Atmospheric ions and nucleation: a review of observations
    Hirsikko A, Nieminen T, Gagné S, Lehtipalo K, H. E. Manninen, Ehn M, Hõrrak U, Kerminen V.-M, Laakso L, P. H. McMurry, Mirme A, Mirme S, Petäjä T, Tammet H, Vakkari V, Vana M, Kulmala M
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    ABSTRACT: This review is based on ca. 260 publications, 93 of which included data on the temporal and spatial variation of the concentration of small ions (<1.6 nm in diameter) especially in the lower troposphere, chemical composition, or formation and growth rates of sub-3 nm ions. This information was collected on tables and figures. The small ions exist all the time in the atmosphere, and the average concentrations of positive and negative small ions are typically 200–2500 cm−3. However, concentrations up to 5000 cm−3 have been observed. The results are in agreement with observations of ion production rates in the atmosphere. We also summarised observations on the conversion of small ions to intermediate ions, which can act as embryos for new atmospheric aerosol particles. Those observations include the formation rates (J2[ion]) of 2-nm intermediate ions, growth rates (GR[ion]) of sub-3 nm ions, and information on the chemical composition of the ions. Unfortunately, there were only a few studies which presented J2[ion] and GR[ion]. Based on the publications, the formation rates of 2-nm ions were 0–1.1 cm−3 s−1, while the total 2-nm particle formation rates varied between 0.001 and 60 cm−3 s−1. Due to small changes in J2[ion], the relative importance of ions in 2-nm particle formation was determined by the large changes in J2[tot], and, accordingly the contribution of ions increased with decreasing J2[tot]. Furthermore, small ions were observed to activate for growth earlier than neutral nanometer-sized particles and at lower saturation ratio of condensing vapours.
    Atmospheric Chemistry and Physics. 01/2011;
  • Source
    Article: An improved criterion for new particle formation in diverse atmospheric environments
    Kuang C, Riipinen I, Sihto S.-L, Kulmala M, A. V. McCormick, P. H. McMurry
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    ABSTRACT: A dimensionless theory for new particle formation (NPF) was developed, using an aerosol population balance model incorporating recent developments in nucleation rates and measured particle growth rates. Based on this theoretical analysis, it was shown that a dimensionless parameter LΓ, characterizing the ratio of the particle scavenging loss rate to the particle growth rate, exclusively determined whether or not NPF would occur on a particular day. This parameter determines the probability that a nucleated particle will grow to a detectable size before being lost by coagulation with the pre-existing aerosol. Cluster-cluster coagulation was shown to contribute negligibly to this survival probability under conditions pertinent to the atmosphere. Data acquired during intensive measurement campaigns in Tecamac (MILAGRO), Atlanta (ANARChE), Boulder, and Hyytiälä (QUEST II, QUEST IV, and EUCAARI) were used to test the validity of LΓ as an NPF criterion. Measurements included aerosol size distributions down to 3 nm and gas-phase sulfuric acid concentrations. The model was applied to seventy-seven NPF events and nineteen non-events (characterized by growth of pre-existing aerosol without NPF) measured in diverse environments with broad ranges in sulfuric acid concentrations, ultrafine number concentrations, aerosol surface areas, and particle growth rates (nearly two orders of magnitude). Across this diverse data set, a nominal value of LΓ=0.7 was found to determine the boundary for the occurrence of NPF, with NPF occurring when LΓ<0.7 and being suppressed when LΓ>0.7. Moreover, nearly 45% of measured LΓ values associated with NPF fell in the relatively narrow range of 0.1<LΓ<0.3.
    Atmospheric Chemistry and Physics. 01/2010;
  • Source
    Article: Atmospheric ions and nucleation: a review of observations
    Hirsikko A, Nieminen T, Gagné S, Lehtipalo K, H. E. Manninen, Ehn M, Hõrrak U, V.-M. Kerminen, Laakso L, P. H. McMurry, Mirme A, Mirme S, Petäjä T, Tammet H, Vakkari V, Vana M, Kulmala M
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    ABSTRACT: This review is based on ca. 250 publications, from which 92 published data on the temporal and spatial variation of the concentration of small ions (<1.6 nm in diameter) in the atmosphere, chemical composition, or formation and growth rates of sub-3 nm ions. The small ions exist all the time in the atmosphere, and the average concentrations of positive and negative small ions are typically 200–2500 cm−3. However, concentrations up to 5000 cm−3 have been observed. The results are in agreement with observations of ion production rates in the atmosphere. Concentrations of small ions increased in the early morning hours due to night time inversion, which leads to accumulation of radon. We also summarised observations on the conversion of small ions to intermediate ions, which can act as embryos for new atmospheric aerosol particles. Those observations include the formation rates (J2[ion]) of 2-nm intermediate ions, growth rates (GR[ion]) of sub-3 nm ions, and information on the chemical composition of the ions. Unfortunately, there were only a few studies which presented J2[ion] and GR[ion]. Based on the publications, the formation rates of 2-nm ions were 0–1.1 cm−3 s−1, while the total 2-nm particle formation rates varied between 0.001 and 60 cm−3 s−1. The ion-mediated processes were observed to dominate when the total particle formation rates were small, and, accordingly the importance of ion-induced mechanisms decreased with increasing total 2-nm particle formation rates. Furthermore, small ions were observed to activate for growth earlier than neutral nanometer-sized particles and at lower saturation ratio of condensing vapours.
    Atmospheric Chemistry and Physics Discussions. 01/2010;
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