Wildfires impact on surface nitrogen oxides and ozone in Central Italy

AbstractA summer campaign in Central Italy was carried out to study the impact of fire emissions on the mixing ratios of surface trace gases. Observations with a selective and sensitive instrument that uses the laser induced fluorescence technique for direct measurements of nitrogen dioxide (NO2), show a significant increase of NO2 mixing ratios, in the evening, when a fire plume reached the observations site. The increase of NO2 mixing ratios is well correlated (R=0.83) with that of particulate matter (PM), which is one of the primary product of forest and grassland fires. The tight correlation between NO2 and PM is used to improve the performance of a statistical regression model to simulate the observed O3, and to highlight the effect of fire emissions on the O3 mixing ratios. The statistical regression model of O3 improves in terms of performance (bias reduction of 77% and agreement enhancement of 10% for slope and correlation coefficient) when PM2.5 is included as additional input and proxy of the fire emissions among the usual input parameters (meteorological data and NO2 mixing ratios). A case study, comparing observed and modeled O3 in different days (with and without fire plume), suggests an impact of fire emissions on the O3 mixing ratios of about 10%

Mesure des radicaux OH et HO2 dans l atmosphère en utilisant la technique FAGE (Développement et mesures de terrain)

Les radicaux HOx (=OH+HO2) jouent un rôle central dans la dégradation des hydrocarbures dans la troposphère. La réaction d OH avec les hydrocarbures mène en présence de NOx à la formation de polluants secondaires comme l ozone. Du fait de sa réactivité élevée, la concentration en OH (<1 ppt) ainsi que son temps de vie (<1 s) sont faibles. Pour valider les modèles de chimie atmosphérique, le développement d appareils capable de mesurer ces très faibles concentrations est nécessaire. Un appareil basé sur la technique FAGE (Fluorescence Assay by Gas Expansion) a été développé à l Université de Lille pour la mesure simultanée des radicaux HOx. La limite de détection atteinte est de 4 . 10[puissance 5] cm-3 pour OH and et 5 . 10[puissance 6] cm-3 pour HO2 pour un temps de mesure de 1 min. L appareil a été utilisé dans 4 campagnes de mesure dans différents environnements : en chambre de simulation, en milieu rural, en milieu urbain et à l intérieur d une classe. Le FAGE de Lille a été validé grâce à 2 intercomparaisons en chambre de simulation et en air ambiant. En parallèle, le FAGE a été adapté pour la mesure de la réactivité d OH. La réactivité d OH est l inverse du temps de vie. L air ambiant est échantillonné au travers d une cellule de photolyse dans laquelle OH est produit. La décroissance d OH mesurée est due à la réaction de OH avec les réactifs présents dans l air ambiant. L appareil de mesure de la réactivité d OH a participé à une campagne de mesure où il a été intercomparé. De plus, la réaction entre NO2* et H2O comme nouvelle source potentielle d OH a été étudiée.HOx(=OH+HO2) radicals play a central role in the degradation of hydrocarbons in the troposphere. Reaction of OH with hydrocarbons leads in the presence of NOx to the formation of secondary pollutants such as O3. Due to its high reactivity, the concentration of OH radicals (<1ppt) and its lifetime are very low (<1s). In order to validate atmospheric chemistry models, the development of highly sensitive instruments for the measurement of OH and HO2 is needed. An instrument based on the FAGE technique (Fluorescence Assay by Gas Expansion) was developed at the University of Lille for the simultaneous measurement of HOx radicals. The limit of detection for OH and HO2 is of 4 . 10[power 5] cm-3 and 5 . 10[power 6] cm-3 respectively for 1 min integration time, appropriate for ambient measurements. The instrument was deployed in 4 field campaigns in different environments: simulation chamber, rural, suburban and indoor. The Lille FAGE was validated during 2 intercomparative measurements in an atmospheric chamber and in ambient air. In parallel, the FAGE set-up was adapted for the measurement of the OH reactivity. OH reactivity is the measure of the total loss of OH radicals that includes the reaction of all chemical species with OH. Ambient air is sampled through a photolysis cell where OH is artificially produced and it decays from the reaction with reactants present in ambient air is recorded by LIF in the FAGE. The OH reactivity system was deployed during an intercomparative measurement and used for the study of the reaction between NO2* and H2O as a source of OH.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Near-Surface Vertical Profiles of Urban Roadside NOx and Fine Particles

This paper presents daytime vertical profiles of the NO[x] concentration, and the number concentration and size distribution of fine particles near a major road in urban Tokyo during spring 2011. No significant height dependence was observed in the NO[x] concentration, presumably due to rapid diffusion. In contrast, the number concentration of particles under 0.5 µm diameter demonstrated an exponential decrease with increasing height above ground level. Vertical profiles derived from this study differ from those presented in previous studies, however, these differences may potentially be explained by the different tailpipe positions of Japanese and US heavy vehicles, as well as the meteorological conditions. This study demonstrates that in Tokyo, the fine particle concentration at 0.5 m above ground level was about 2.9 times higher than that at 2.0 m. The higher fine particle concentration immediately above ground level implies that children may be at greater risk of experiencing pollutant-related respiratory symptoms than adults

Rate constants of the reaction of C 2 –C 4 peroxy radicals with OH radicals

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