Modeled aerosol dry deposition velocities to natural surfaces have not been verified against experimental data because data is not available. However due to recent instrumentation developments measuring vertical number fluxes of aerosols with sizes down to 10 nm became possible. Additional instrument modifications which are discussed here allows measuring size dependent fluxes of 10-100 nm aerosols and would fulfill the data gap. This study analyzes uncertainties in such measurements. Low particle count is identified as a major contributor to the measurement uncertainty, limiting the accurate estimation of size-resolved dry deposition velocities in remote environment to particles with diameters less than 50 nm using current instrumentation. Even in this size range high concentrations are required. In the case of two particle counters with different detection limits dry deposition velocity estimates can be also systematically biased, depending on the aerosol size distribution. A difference in detection limits of counters about 10 nm is narrow enough to avoid bias in size-dependent dry deposition velocities in most circumstances. Published by Elsevier Science Ltd.