During the poke-flow experiments, the particles were exposed to a constant flow of gas, which could lead to the evaporation of semi-volatile organic compounds (SVOCs). A loss of SVOCs by evaporation would lead to an increase in the viscosity of the SOA particles. To estimate SVOC loss, the cross-sectional area of several particles was measured over ~24 h (Fig. ). In all cases, the change in cross-sectional area was less than the uncertainty in the measurement except for experiments with guaiacol + OH, which had a change in area of -8.3 ± 4.2% and -9.9 ± 9.1% after 24 h of conditioning (Fig. ). Considering all the evaporation experiments together and the uncertainties in measuring the cross-sectional area, we conclude that the evaporation of SVOCs during conditioning was relatively small. This is consistent with expectations based on the volume of air the particles were exposed to in the environmental chamber (~2.5 × 10 4 L) compared to during conditioning (conservatively < 3.0 × 10 3 L).