The Model 310 is a 300 L/min, medium flow air sampler consisting of an inlet, a PM10 and a PM2.5 virtual impactor for size separation of airborne particles, a final filter, and a polyurethane foam (PUF) sampler to collect organic vapors downstream of the filter. The modular design allows the system to be used for PM10, PM2.5, or PM10/PM2.5 dichotomous sampling. The system also includes a blower, blower speed control, and instrumentation for flow measurement. A seven-day solid-state timer allows up to 14 programmable starts and stops of the system. For instance, the timer can be programmed to collect day-time samples from 6:00 a.m. to 6:00 p.m. each day for a whole week, so that a weekly total sample can be obtained.