I am looking for a reference suggesting values or algorithms to estimate deposition velocity of PM10 on rainy days.
Hello Mahyar, the in-cloud and below-cloud scavenging rates depend on particle size. Therefore, the values for PM10 can differ from time to time, place to place depending on the particle size distribution. If you look for useful papers, I can recommend the work by Constantin Andronache , Boston College. He has written several papers on the topic. We have tried ourselves to verify his deposition rates experimentally by using atmospheric long-term observations or particle size distributions in three different places, linking them by trajectories. The paper can be found here: Article Aerosol connections between three distant continental stations
We confirm deposition rates in the mass-dominating accumulation mode to be around 4*10^-5 s^-1. However, this is for Central Europe with plenty of stratiform precipitation events. I could imagine that deposition velocities in a tropical rain events could be quite different. Kind regards, Wolfram
Hello Mahyar
I did some calculation years ago...
Article Estimation of the particle and gas scavenging contributions ...
Particle velocities were estimated using the conventional calculation scheme proposed by Hinds (Aerosol Technology). It worked well to predict rainwater concentrations using our estimations for scavenging coefficients.
Blessings,
Silvia
We use a very simple approximation of the wet scavenging rate of PM10 in the urban air quality model EPISODE-CityChem (Article The Eulerian urban dispersion model EPISODE. Part II: Extens...
, Appendix B) which is based on the EMEP status report 1/2003 [Simpson, D., Fagerli, H., Jonson, J. E., Tsyro, S., and Wind, P.: Transboundary Acidification, Eutrophication and Ground Level Ozone in Europe. Part 1: Unified EMEP Model Description, EMEP Status Report 1/2003, ISSN 0806-4520, Norwegian Meteorological Institute, Oslo, Norway, 2003].! RHO_W - Density of rain water (1000 kg m^-3).
! V_drop - Raindrop fall speed (5 m/s).
! A_MA_PA - Empirical coefficient assuming a Marshall-Palmer size
! distribution for the rain drops (5.2 m^3 kg^-1 s^-1).
! E_C_EFF - The size dependent collection efficiency of
! aerosols by the raindrops (dimless)
! (= 0.4 for PM10 here)
! PRECV - precipitation in m/s
RHO_W = 1000.0
V_drop = 5.0
A_MA_PA = 5.2
E_C_EFF = 0.4
C_FAC1 = RHO_W * A_MA_PA / V_drop
C_FAC2 = C_FAC1 * E_C_EFF
WDEPRATE = C_FAC2 * PRECV
It would be interesting to hear what values of the PM10 collection efficiency others are using. This simplistic approach treats in-cloud scavenging in the same way as below-cloud scavenging. We are mainly interested in the urban areas. For the short-term estimation of near-ground concentrations in urban areas, below-cloud scavenging is expected to be the dominant wet removal process.
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