Dalton's Law of partial pressures and the hypothesis that water vapor equilibrium above a canister surface is identical to that established above liquid water are used to predict the variation of the percent relative humidity (percentRH) of air released from canisters used in ambient air sampling, typically 6L canisters pressurized with 18L of air. During sampling, some water vapor is adsorbed on the canister wall. When (and if) the water vapor partial pressure exceeds its saturation vapor pressure, water vapor condensation begins and the condensation rate equals the sampling rate of water vapor into the canister. Under constant temperature conditions, the air subsequently released from the canister is less humid than the original sample, following the relationship, percentRH = 100percent (6L/V_s) for V_s>V_r where V_s is the residual air volume and V_r is the residual air volume at which water is completely removed (except for adsorbed water vapor) from the canister wall. For V_s展开▼
