Heterogeneous uptake of NO2 on soils under variable temperature and relative humidity conditions

Heterogeneous reactions of nitrogen dioxide (NO2) on soils collected from Dalian (S1) and Changsha (S2) were investigated over the relative humidity (RH) range of 5%–80% and temperature range of 278–328 K using a horizontal coated-wall flow tube. The initial uptake coefficients of NO2 on S2 exhibited a decreasing trend from (10 ± 1.3) × 10−8 to (3.1 ± 0.5) × 10−8 with the relative humidity increasing from 5% to 80%. In the temperature effect studies, the initial uptake coefficients of S1 and S2 decreased from (10 ± 1.2) × 10−8 to (3.8 ± 0.5) × 10−8 and from (16 ± 2.2) × 10−8 to (3.8 ± 0.4) × 10−8 when temperature increased from 278 to 288 K for S1 and from 278 to 308 K for S2, respectively. As the temperature continued to increase, the initial uptake coefficients of S1 and S2 returned to (7.9 ± 1.1) × 10−8 and (20 ± 3.1) × 10−8 at 313 and 328 K, respectively. This study shows that relative humidity could influence the uptake kinetics of NO2 on soil and temperature would impact the heterogeneous chemistry of NO2.