Influences of outdoor meteorological conditions on indoor wintertime short-term PM1 levels

We investigated the relationship between wintertime 1-min mean urban indoor particulate matter mass concentrations for particles with aerodynamic diameter of < 1 μm (PM1) and outdoor atmospheric conditions. Particle concentrations were measured by two light-scattering laser photometers. Aerosol monitors were placed in the ground and first floor corridors of an university building, with inlets at heights of 1.7 m above the floor. The building is located in residential area of Zagreb, Croatia. During the experiment usual student and employee activities were occurring within the building. Surface meteorological data were collected at a nearby outdoor location. Results show the dependence of indoor PM1 on outdoor meteorology, with the strongest responses to air temperature and relative humidity, whilst global radiation impacts were almost negligible. Response times varied from 1.2 hours (for relative humidity) to 2.7 days (for global radiation). Furthermore, elevated mean concentrations point to the 8–9 km distant industrial zone. Both, PM1 and meteorological data series exhibited semidiurnal, diurnal and the long-term (about 10–11 days and about 21 day) periodicity. The long-term periodicity of PM1 time series might be associated with Rossby waves. Possible association with Rossby waves needs to be investigated further.