The interaction of N2O5 with mineral dust: aerosol flow tube and Knudsen reactor studies

The interaction of mineral dust with N2O5 was investigated using both airborne mineral aerosol (using an aerosol flow reactor with variable relative humidity) and bulk samples (using a Knudsen reactor at zero humidity). Both authentic (Saharan, SDCV) and synthetic dust samples (Arizona test dust, ATD and calcite, CaCO3) were used to derive reactive uptake coefficients (gamma). The aerosol experiments (Saharan dust only) indicated efficient uptake, with e. g. a value of gamma (SDCV)=(1.3 +/- 0.2) x 10(-2) obtained at zero relative humidity. The values of gamma obtained for bulk substrates in the Knudsen reactor studies are upper limits due to assumptions of available surface area, but were in reasonable agreement with the AFT measurements, with: gamma (SDCV)=(3.7 +/- 1.2) x 10(-2), gamma (ATD)=(2.2 +/- 0.8) x 10(-2) and gamma (CaCO3)=(5 +/- 2) x 10(-2). The errors quoted are statistical only. The results are compared to literature values and assessed in terms of their impact on atmospheric N2O5.