Evaporative losses of fine particulate nitrates during sampling

Laboratory and field data for losses of nitrates during sampling with filters and impactors are compared with theoretical predictions for evaporative losses. Predicted sampling efficiencies are in qualitative agreement with measured values. Both theoretical analysis and experimental data indicate that significant nitrate losses from filters and impactors can occur, although losses from impactors are far less than from filters. For both types of sampler, evaporative losses increase as the ratio of the gas-phase concentration to the particle concentration increases. For filters, losses become significant when this ratio exceeds a value in the range of 0.1-1.0; a value in the range 1.0-10.0 is required for losses to be significant for impactors.