Description of Instrument Model.

This page provides access to the latest version of the Droplet Measurement Technologies Continuous Flow Streamwise Thermal Gradient (CFSTGC) CCN chamber model. The code simulates droplet growth in the instrument while fully accounting for water vapor depletion effects (Lathem and Nenes, 2011), changes in the instrument operation parameters, and dry particle properties (hygroscopicity and dry size distributions). The updated model is more reliable and faster by an order of magnitude than the versions used in the studies of Lathem and Nenes (2011), Lance et al. (2006) and Roberts and Nenes (2005), and is further accelerated by two orders of magnitude if developed velocity profiles are assumed (without significant loss of accuracy in predicted supersaturation and droplet size; Raatikainen et al., 2012). The latter configuration makes the model suitable for analyzing large data sets. Model accuracy was verified by a detailed comparison with ammonium sulfate calibration data covering a wide range of instrument operation parameters.

The model can be used in a number of applications; the prime (and perhaps most challenging) of which is its usage to study CCN activation kinetics with the approach of Raatikainen et al. (2012). For this, dry particle size distributions and hygroscopicity of the aerosol flowing in the instrument needs to be known, as well as the instrument operation parameters (temperatures, flow rates and pressure obtained from the CCN instrument files) and the supersaturation from calibration experiments (e.g., Rose et al., 2008; Moore et al., 2010). Careful OPC calibration and possibly also tuning of model parameters (e.g. measuring and using accurate sheath flow RH) are needed to obtain accurate absolute numerical values for the water vapor uptake coefficient. A simpler application of the model, which does not require any additional calibrations or model tuning, is predicting relative changes in droplet size from the effects not related to water vapor uptake (changes in instrument operation parameters, water vapor depletion and changes in dry particle properties). This method was used in two applications (Raatikainen et al., 2012; Moore et al., 2012), of updated model on real ambient CCN measurements. In both cases, the model has shown the importance of water vapor depletion effects on droplet size. If unaccounted for, the effect of water vapor depletion could have been (incorrectly) interpreted as a change in the water vapor uptake coefficient.

Most of the past CCN studies using the CFSTGC have focused on CCN concentrations and hygroscopicity but have largely ignored the droplet sizing capability of the instrument. As a result, there is a large amount of unanalyzed droplet size data from chamber experiments and field measurements worldwide. The model posted here, together with the approach outlined by Raatikainen et al. (2012) allow the extraction of CCN activation kinetics from this data, and, will enable the development a much-needed climatology of CCN activation kinetics.

Downloading the CFSTGC model package

Notice: By downloading these codes, you agree to abide with these terms of usage. If you do not agree to any of these terms, you may not download or use any portion of the CSTGC package.

- CFSTGC model package (CFSTGC_Package.zip) that includes CFSTGC simulator for data generated by the TSI AIM and DMT CCNc control software (Last updated: January 20, 2012)

- CFSTGC demo data set (CFSTGC_Demo.zip) described in the manual. (Last updated: January 20, 2012)

- CFSTGC model manual (Last updated: January 20, 2012 ).

Development history and acknowledgments

All the codes are written in FORTRAN can run on virtually any platform with a FORTRAN compiler. The executables provided on this page have been compiled with Lahey FORTRAN v5.6 and can run on any Windows platform (from XP and on). The codes were written by AN and TR.

We would like to thank funding support from the Finnish Cultural Foundation. We also acknowledge support from a NSF Graduate Student Fellowship, an NSF CAREER award, DOE Global Change Education Program, the DOE STTR program, a NASA Earth and Space Science Graduate Research Fellowship, and NOAA. We thank G. Kok and R. Drgac from Droplet Measurement Technologies for their support and advice on calibration of the OPC. We also thank T.Lathem and R.Moore for their feedback on the package.

References

Raatikainen, T., Moore, R. H., Lathem, T. L. and A. Nenes (2012) A coupled observation– modeling approach for studying activation kinetics from measurements of CCN activity, Atmos.Chem.Phys., in review

Moore, R.H., Raatikainen, T., Langridge, J.M., Bahreini, R., Brock, C.A., Holloway, J.S., Lack, D.A., Middlebrook, A.M., Perring, A.E., Schwarz, J.P., Spackman J.R., and Nenes, A. (2012) CCN Spectra, Hygroscopicity, and Droplet Activation Kinetics of Secondary Organic Aerosol Resulting from the 2010 Deepwater Horizon Oil Spill, Env.Sci.Tech., in review

Lathem, T.L and Nenes, A. (2011) Water vapor depletion in the DMT Continuous Flow CCN Chamber: effects on supersaturation and droplet growth, Aeros.Sci.Tech., 45, 604–615, doi:10.1080/02786826.2010.551146 (Preprint, Journal reprint, erratum) Note

Moore., R., Nenes, A., and Medina, J. (2010) Scanning Mobility CCN Analysis - A method for fast measurements of size resolved CCN distributions and activation kinetics, Aeros.Sci.Tech., 44, 861-871 (Preprint, Journal reprint) Note

Rose, D., Gunthe, S., Mikhailov, E., Frank, G., Dusek, U., Andreae, M., and Poschl, U. (2008). Calibration and Measurement Uncertainties of a Continuous-Flow Cloud Condensation Nuclei Counter (DMT-CCNC): CCN Activation of Ammonium Sulfate and Sodium Chloride Aerosol Particles in Theory and Experiment, Atmos. Chem. Phys., 8:1153–1179.

Lance, S., Medina, J., Smith, J.N., Nenes, A. (2006) Mapping the Operation of the DMT Continuous Flow CCN Counter, Aeros.Sci.Tech., 40, 242-254 (Preprint, Journal reprint) Note

Roberts, G., and Nenes, A. (2005) A Continuous-Flow Streamwise Thermal-Gradient CCN Chamber for Atmospheric Measurements, Aerosol Science and Technology, 39, 206–221, doi:10.1080/027868290913988 (Preprint, Journal reprint) Note

More information? Try these links:

Instrumentation and techniques

Laboratory and field studies

Athanasios Nenes Webpage

Comments or Questions? Contact athanasios.nenes@gatech.edu

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