New particle formation and condensational growth in a large indoor space

Several episodes of new particle formation followed by slow condensational growth were observed in a large construction hall during a routine measurement of air quality in May of 2007. Both nucleation and growth resembled those processes in the outside, open atmosphere. Appearance near midday, relative indoor humidity below 50% and outdoor ozone concentration above 100 μg m−3 were characteristic for nucleation events. Condensational growth rates were about 2.6 nm h−1, close to those recorded at a rooftop station in an urban atmosphere in Prague. In the hall, the growths were frequently interrupted by the activity of personnel during work shifts. Outside of the work shifts, one case of undisturbed growth lasting for 18 h was recorded. Although the penetration of particles from outdoors is a possible explanation for the aerosol nucleation and growth, the low value of the air exchange rate (0.36 h−1), high number concentrations and long residence time of aerosol particles in a large hall allow us to hypothesize the whole process started and evolved indoors. This hypothesis has two important implications. New particle formation and growth can also be considered as a micro-scale phenomenon, and processes of atmospheric aerosol nucleation and growth can be studied under semi-experimental conditions in large indoor spaces.