An enclosure or housing for an air monitoring instrument package for mounting on the roof or other surface on the outside of vehicles such as cars, trucks, buses, trams, trains and ships. By measuring air pollutants from moving vehicles, it is possible to explore the distribution of air pollutants throughout a city or rural area for the identification of sources of different pollutants, estimating human exposures to air pollutants, and mapping air pollutants with high resolution. The disclosed device provides continuous sampling of outside air while simultaneously protecting the delicate instruments from weather elements such as high wind, rain, snow, sleet and hail. The design also allows a nearly constant flow rate of sampled air independent of vehicle velocity. An optional impaction region further reduces transmission of mist and large particles to the chamber containing the measurement package.