Atmos. Chem. Phys., 14, 3729-3737, 2014
http://www.atmos-chem-phys.net/14/3729/2014/ doi:10.5194/acp-14-3729-2014 © Author(s) 2014. This work is distributed under the Creative Commons Attribution 3.0 License. |

Technical note

11 Apr 2014

Air Quality Research Division, Science and Technology Branch, Environment Canada, Toronto, Canada

Received: 24 Sep 2013 – Published in Atmos. Chem. Phys. Discuss.: 02 Dec 2013

Revised: 12 Feb 2014 – Accepted: 06 Mar 2014 – Published: 11 Apr 2014
Abstract. An empirical algorithm is developed for calculating bulk dry deposition velocity (*V*_{d}) of fine (PM_{2.5}) – particles having a diameter of ≤ 2.5 μm), coarse (PM_{2.5−10} – particles having a diameter of 2.5–10 μm), and giant (PM_{10+} – particles having a diameter of > 10 μm) atmospheric particles. The algorithm is developed from an empirical fit of *V*_{d} data calculated using the size-resolved *V*_{d} scheme of Zhang et al. (2001) with assumed lognormal size distributions of PM_{2.5}, PM_{2.5−10} and PM_{10+}. In the new algorithm, the surface deposition velocity (*V*_{ds}) is parameterized as a simple linear function of friction velocity (*u*_{*}) for PM_{2.5} and as a polynomial function of *u*_{*} for both PM_{2.5−10} and PM_{10+} over all the 26 land use categories (LUCs). An adjustment factor as an exponential function of *u*_{*} and leaf area index (LAI) is also applied to *V*_{ds} of PM_{2.5−10} and PM_{10+} over 9 of the 26 LUCs that have variable LAI. Constant gravitational settling velocities are provided for PM_{2.5}, PM_{2.5−10} and PM_{10+}. Aerodynamic resistance between a reference height and the surface can be calculated using available analytical formulas from the literature. The bulk *V*_{d} of PM_{2.5}, PM_{2.5−10} and PM_{10+} at the reference height can then be calculated by combining the gravitational settling velocity, aerodynamic resistance and the parameterized *V*_{ds}. *V*_{d} values calculated using the new algorithm are within ±20% of those using the original size-resolved scheme for fine, coarse and giant particles. Uncertainties in *V*_{d} values from the new algorithm due to the pre-assumed size distributions are on the order of 20% for fine particles and on the order of a factor of 2.0 for coarse and giant particles. The new algorithm provides an alternative approach for calculating *V*_{d} of bulk aerosol particles. *V*_{d} of any particulate species can be simply estimated using this scheme as long as the mass fractions in fine, coarse and giant particles are known or can be assumed.

**Citation:**
Zhang, L. and He, Z.: Technical Note: An empirical algorithm estimating dry deposition velocity of fine, coarse and giant particles, Atmos. Chem. Phys., 14, 3729-3737, doi:10.5194/acp-14-3729-2014, 2014.