Conversion of NO2, HNO2 gas, their mixture and a mixed gas of HNO2 and HNO3
on silica particles was investigated under simulated atmospheric condition
s. Both HNO2 and HNO3 were detected as the products from conversion of NO2
on silica particles. However, unlike HNO3, which increased with conversion
time, HNO2 underwent an increase-decrease time course due to the increased
HNO3 further transformed HNO2 into NO+ on silica particles. Considering the
catalytic effect of HNO3 and HNO2 on the nitration of pyrene adsorbed on s
ilica particles by NO2, another electrophilic nitration path, analogous to
the one that we previously reported, with NONO2+ and NON2O4+ as electrophil
es was suggested. The two paths together gave an appropriate explanation fo
r the catalytic effect of HNO2, HNO3 and their mixed gas on the nitration o
f the adsorbed pyrene by NO2. (C) 2000 Elsevier Science Ltd. All rights res
erved.