INDOOR OUTDOOR CONCENTRATIONS OF OZONE AND PEROXYACETYL NITRATE (PAN)

Photochemical pollutants such as ozone and peroxyacetyl nitrate (PAN) could adversely affect human health, especially with relation to effec ts on lung function. For a realistic assessment of ambient concentrati ons, both outdoor and indoor measurements of ozone and PAN are require d, because people stay indoors for most of the time. Indoor/outdoor co ncentration ratios, indoor half-life times and indoor chemistry includ ing physicochemical reactions on surfaces are quite well known for ozo ne, but not for PAN. While ozone is removed very rapidly mainly by het erogeneous reactions on surfaces or by gasphase reactions with e.g. ca rpet emissions, no such processes are known for PBN at present. The ma in removal process for PAN is thermal decay. Indoor concentrations of ozone and PAN can be a significant fraction of those outdoors highly d epending on the ventilation pattern. Our measurements in various kinds of non-air-conditioned rooms show maximal indoor concentrations betwe en 80 and 100% of those outdoors for ozone and PAN, respectively. Aver age indoor/outdoor ratios were calculated of 0.5 for ozone and between 0.7 and 0.9 for PAN. The half-life times ranged between only a few mi nutes fur ozone and 0.5 to 1 h for PAN.