A cost-effective weighing chamber for particulate matter filters

Particulate matter (PM) is a ubiquitous air pollutant that has been receivi ng increasing attention in recent years due in part to the association betw een PM and a number of adverse health outcomes, including mortality and inc reases in emergency room visits and respiratory symptoms, as well as exacer bation of asthma and decrements in lung function.(1-5) As a result, the abi lity to accurately sample ambient PM has become important, both to research ers and to regulatory agencies. The federal reference method for the determ ination of fine PM as PM2.5. in the atmosphere recommends that particle-sam pling filters be conditioned and weighed in an environment with constant te mperature and relative humidity (RH).(6) It is also recommended that vibrat ion, electrostatic charges, and contamination of the filters from laborator y air be minimized to reduce variability in filter weight measurements. The se controls have typically been maintained in small, environmentally contro lled "cleanrooms. " As an alternative to constructing an elaborate cleanroo m, we have designed, and presented in this paper, an inexpensive weighing c hamber to maintain the necessary level of humidity control.