Aerosol number to volume ratios in Southwest Portugal during
                        ACE-2

Dusek, Ulrike; Covert, David S.; Wiedensohler, Alfred; Neusüß, Christian; Weise, Diana

doi:10.3402/tellusb.v56i5.16461

Cited by 4 publications

(10 citation statements)

References 14 publications

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“…Specifically for modal models, the general mathematical formulation of the size distribution for each aerosol mode is prescribed such that when the mass and number concentration (and in certain cases surface area or sixth moment) of a given mode are predicted, the distribution is fully defined [e.g., Binkowski and Shankar , 1995; Harrington and Kreidenweis , 1998; Wilson et al , 2001; Liu et al , 2005; Stier et al , 2005]. It is consistent with field measurement results that aerosols generally have multiple modes in their size distribution, which can be approximated using a lognormal size distribution [e.g., Cantrell and Whitby , 1978; John et al , 1990; Berner et al , 1996; Bond et al , 2004; Clarke et al , 2004; Dusek et al , 2004].…”

Section: Introductionsupporting

confidence: 70%

Distribution and direct radiative forcing of carbonaceous and sulfate aerosols in an interactive size‐resolving aerosol–climate model

et al. 2008

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[1] A multimode, two-moment aerosol model has been incorporated in the NCAR CAM3 to develop an interactive aerosol-climate model and to study the impact of anthropogenic aerosols on the global climate system. Currently, seven aerosol modes, namely three for external sulfate and one each for external black carbon (BC), external organic carbon (OC), sulfate/BC mixture (MBS; with BC core coated by sulfate shell), and sulfate/OC mixture (MOS; a uniform mixture of OC and sulfate) are included in the model. Both mass and number concentrations of each aerosol mode, as well as the mass of carbonaceous species in the mixed modes, are predicted by the model so that the chemical, physical, and radiative processes of various aerosols can be formulated depending on aerosol's size, chemical composition, and mixing state. Comparisons of modeled surface and vertical aerosol concentrations, as well as the optical depth of aerosols with available observations and previous model estimates, are in general agreement. However, some discrepancies do exist, likely caused by the coarse model resolution or the constant rates of anthropogenic emissions used to test the model. Comparing to the widely used mass-only method with prescribed geometric size of particles (one-moment scheme), the use of prognostic size distributions of aerosols based on a two-moment scheme in our model leads to a significant reduction in optical depth and thus the radiative forcing at the top of the atmosphere (TOA) of particularly external sulfate aerosols. The inclusion of two types of mixed aerosols alters the mass partitioning of carbonaceous and sulfate aerosol constituents: about 35.5%, 48.5%, and 32.2% of BC, OC, and sulfate mass, respectively, are found in the mixed aerosols. This also brings in competing effects in aerosol radiative forcing including a reduction in atmospheric abundance of BC and OC due to the shorter lifetime of internal mixtures (cooling), a mass loss of external sulfate to mixtures (warming), and an enhancement in atmospheric heating per BC mass due to the stronger absorption extinction of the MBS than external BC (warming). The combined result of including a prognostic size distribution and the mixed aerosols in the model is a much smaller total negative TOA forcing (À0.12 W m À2 ) of all carbonaceous and sulfate aerosol compounds compared to the cases using one-moment scheme either excluding or including internal mixtures (À0.42 and À0.71 W m À2 , respectively). In addition, the global mean all-sky TOA direct forcing of aerosols is significantly more positive than the clear-sky value due to the existence of low clouds beneath the absorbing (external BC and MBS) aerosol layer, particularly over a dark surface. An emission reduction of about 44% for BC and 38% of primary OC is found to effectively change the TOA radiative forcing of the entire aerosol family by À0.14 W m À2 for clear-sky and À0.29 W m À2 for all-sky.Citation: Kim, D., C. Wang, A. M. L. Ekman, M. C. Barth, and P. J. Rasch (2008), Distribution and direct radiative forci...

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Section: Introductionsupporting

confidence: 70%

Distribution and direct radiative forcing of carbonaceous and sulfate aerosols in an interactive size‐resolving aerosol–climate model

et al. 2008

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“…In air where Aitken mode is prominent, the values of R (0.1 μ m) are larger, being usually in the range 200–300 μ m −3 . However, more extreme cases have also been reported, R (0.1 μ m) being less than 50 μ m −3 or more than 500 μ m −3 [ Dusek et al , 2004; Eleftheriadis et al , 2006; Kivekäs et al , 2007] This uncertainty creates a need for more investigations on the behavior of R (0.1 μ m) in different environments.…”

Section: Discussionmentioning

confidence: 99%

“…The main reason for using R ( d c ) in our analysis is that in all aerosol systems investigated so far, this quantity has been found to vary much less than what random size distributions would produce [ Van Dingenen et al , 2000; Hegg and Russell , 2000; Dusek et al , 2004; Eleftheriadis et al , 2006; Kivekäs et al , 2007]. In previous studies the cut‐off diameter d c has been chosen to be between 80 and 120 nm.…”

Section: Approachmentioning

confidence: 99%

Parameterization of cloud droplet activation using a simplified treatment of the aerosol number size distribution

et al. 2008

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[1] The number-to-volume concentration ratio, R, defined as the number concentration of particles larger than a certain cut-off diameter divided by the total particle volume concentration, can be used for expressing aerosol number size distributions in a simplified way. Earlier studies have shown that R shows less variability than random size distributions would produce. In this article the parameter R was used to develop a new parameterization for estimating the cloud droplet number concentration (CDNC). The parameterization is a function of four input parameters: the total submicron volume concentration (V tot ), number-to-volume concentration ratio with a 0.1-mm cut-off diameter (R(0.1 mm)), soluble fraction of the particle volume (e) and air updraft velocity (v up ). The parameterization was derived by finding the best fit to a series of simulations made with an adiabatic air parcel model simulating cloud droplet activation, and the model input parameters were varied over a range typical for northern European background air. Results from the parameterization were compared with cloud droplet concentrations measured in Northern Finland, and a good agreement was found. The new parameterization demonstrates that if the value of R(0.1 mm) can be estimated or parameterized without knowing the whole particle number size distribution, cloud droplet number concentrations can be estimated relatively accurately by using only the four parameters mentioned above. This would reduce significantly the computer resources needed for calculating CDNC in large-scale atmospheric models.

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“…Measurements conducted over marine areas have demonstrated that the particle number (in the CCN size range) to volume concentration ratio is surprisingly constant, especially when considering the relatively large variability in particle number concentrations and size distributions [ Van Dingenen et al , 1999, 2000; Hegg and Jonsson , 2000; Hegg and Russell , 2000; Dusek et al , 2004]. Several reasons for this have been identified.…”

Section: Introductionmentioning

confidence: 99%

“…Second, both condensational growth and cloud processing modify the shape of the accumulation mode in a way that has stabilizing effects on the number to volume ratio [ Hegg and Russell , 2000]. In some cases, this ratio can also be stabilized by the dependence of the Aitken and accumulation parameters on each other [ Dusek et al , 2004].…”

Section: Introductionmentioning

confidence: 99%

Particle number to volume concentration ratios at two measurement sites in Finland

Kivekäs¹,

Kerminen²,

Engler³

et al. 2007

J. Geophys. Res.

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[1] Past studies have indicated that the aerosol number to volume concentration ratio R, defined as the number concentration of particles larger than a certain cutoff diameter divided by the total particle volume concentration, shows little variability in marine conditions. In this study, aerosol number size distributions from Pallas in northern Finland and from the island of Utö in the Baltic Sea, representing more continental aerosol systems, were analyzed. The data set covered continuous measurements for 20 months at Pallas and 21 months at Utö. The average value and standard deviation of R, calculated from the measured data, were found to be inversely dependent on the cutoff diameter used, Also, the relative deviation (standard deviation divided by average value) of R(d c ) was found to be dependent on the cutoff diameter. A clear seasonal pattern of the values of R was observed at both sites, and this was found to be related to ambient temperature. The value of R was found to depend on the air mass type at Pallas, but at Utö such dependency was not observed. Besides temperature, R was also analyzed against several meteorological parameters, including global solar radiation, air pressure, relative humidity, and rain. The found dependencies between the number of potential cloud condensation nuclei and particle volume concentration provide tools for developing more accurate empirical parameterizations describing cloud formation in large-scale atmospheric models.

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Aerosol number to volume ratios in Southwest Portugal during ACE-2

Cited by 4 publications

References 14 publications

Distribution and direct radiative forcing of carbonaceous and sulfate aerosols in an interactive size‐resolving aerosol–climate model

Distribution and direct radiative forcing of carbonaceous and sulfate aerosols in an interactive size‐resolving aerosol–climate model

Parameterization of cloud droplet activation using a simplified treatment of the aerosol number size distribution

Particle number to volume concentration ratios at two measurement sites in Finland

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