Continuous Ambient Mass Monitor

摘要

A Continuous Ambient Mass Monitor (CAMM) for fine particle mass has recently been developed and tested. The principle of this method is based on the measurement of pressure drop across a fibrous filtr (Flouropore~(TM) during particle sampling. The monitor consists of a conventional impactor/inlet to remove particles larger than 2.5 mum, a filter tape to collect particles, a filter tape transportation system to allow for several weeks of unassisted sampling, a diffusion dryer to remove particle-bound water, and a data acquisition and control unit. For each sampling period a new segment of the filter tape is exposed so that particles remain in equilibrium with the sample air during their collection. This results in minimization of volatilization and adsorption artifacts thus rendering this method to be more accurate. Furthermore, since the required flow rate for the fine particle meass monitoring channel is only 0.3 liters/min, the relative humidity of the air sample can be easily reduced to 40percent or less using a Nafion~(TM) diffusion dryer, to remove particlebound water. The sensitivity of the CAMM method for PM_(2.5) is high, with a detection limit of less than 5mug/m~3 for a one-hour mean.