Comparison of laser-induced fluorescence and chemiluminescence measurements of NO2 at an urban site

In situ measurements of nitrogen dioxide (NO2) concentrations were conducted at an urban site in Tokyo (35°71′N, 139°76′E), Japan during the summers of 2007–2009. A chemiluminescence instrument equipped with a molybdenum oxide converter (Mo-CL) and a laser-induced fluorescence (LIF) instrument were used simultaneously for determining the ambient NO2 concentrations. A tight linear correlation between the NO2 concentrations determined by the LIF and Mo-CL techniques was evident except for high ozone concentration periods over 50 ppbv. During the high ozone episodes, correlation plots of the NO2 concentrations between Mo-CL and LIF techniques indicated an overestimation of Mo-CL NO2. To examine in detail the systematic differences between two techniques, a thermal dissociation laser-induced fluorescence (TD-LIF) instrument was employed in the summer of 2009 to measure total peroxy nitrates (ΣPNs) and total reactive nitrogen (NOz). We found that the ΣPNs concentrations correlated well with the discrepancies in NO2 concentrations determined by the Mo-CL and LIF techniques. This result suggests that peroxy nitrate species significantly contribute to the observed interference in the Mo-CL measurements under high O3 concentrations in our observation at the urban site in Tokyo.