Measurements and numerical simulations of indoor O3 and NOx in two different cases

Simultaneous indoor and outdoor measurements of O3, NO, NO2* (NOx NO) that lasted a lot of days, took place in two buildings and were also accompanied by other environmental measurements. The two buildings have bright natural sunlight, similar dimensions but many differences in their design and operation, as well as a different way of ventilation. The one is located in Thessaloniki (LIDAR) while the other is in Athens (PERPA), a city with a much higher level of air pollution. In the PERPA-bldg., indications of hydrocarbon intrusion from an adjacent chemical laboratory were observed. The differences between these two buildings are reflected in the change of behavior of the indoor/outdoor O3, NO, NO2* concentration ratios. In the LIDAR-bldg. there were elevated O3 and NO2* ratios combined with small NO ratios. At the PERPA-bldg. the corresponding ratios, mainly for O3, were influenced for long period by the indoor VOCs source. The O3 concentration ratios are representative of the buildingʹs design, operation and location in case of naturally ventilated and lighted buildings. Also they are a sensitive indicator of the existence of indoor VOCs source. The 24 h peak indoor/outdoor NO concentration ratios reflected the differences between the buildingsʹ air exchange rate, but the 24 h averaged NO ratios seems unaffected by any indoor air quality parameter in this study. The NO2* measurements include the contribution of other nitrogen-containing species, which seems to vary with the building characteristics and with time. With the acquired experimental data for this type of interior locations, the Nazaroff and Cass (1986) mathematical model was tested, which predicts the indoor air pollutant concentrations. The modelʹs results were satisfactory. In addition, it was possible for the theoretical investigation into the causes of the formation of the observed indoor air pollutant concentrations to be undertaken. The indoor NOx chemistry is not affected only by homogeneous but also by heterogeneous reactions, as shown by model results.