Tropospheric Ozone Assessment Report : A critical review of changes in the tropospheric ozone burden and budget from 1850 to 2100

Our understanding of the processes that control the burden and budget of tropospheric ozone has changed dramatically over the last 60 years. Models are the key tools used to understand these changes, and these underscore that there are many processes important in controlling the tropospheric ozone budget. In this critical review, we assess our evolving understanding of these processes, both physical and chemical. We review model simulations from the International Global Atmospheric Chemistry Atmospheric Chemistry and Climate Model Intercomparison Project and Chemistry Climate Modelling Initiative to assess the changes in the tropospheric ozone burden and its budget from 1850 to 2010. Analysis of these data indicates that there has been significant growth in the ozone burden from 1850 to 2000 (approximately 43 + 9%) but smaller growth between 1960 and 2000 (approximately 16 +/- 10%) and that the models simulate burdens of ozone well within recent satellite estimates. The Chemistry Climate Modelling Initiative model ozone budgets indicate that the net chemical production of ozone in the troposphere plateaued in the 1990s and has not changed since then inspite of increases in the burden. There has been a shift in net ozone production in the troposphere being greatest in the northern mid and high latitudes to the northern tropics, driven by the regional evolution of precursor emissions. An analysis of the evolution of tropospheric ozone through the 21st century, as simulated by Climate Model Intercomparison Project Phase 5 models, reveals a large source of uncertainty associated with models themselves (i.e., in the way that they simulate the chemical and physical processes that control tropospheric ozone). This structural uncertainty is greatest in the near term (two to three decades), but emissions scenarios dominate uncertainty in the longer term (2050- 2100) evolution of tropospheric ozone. This intrinsic model uncertainty prevents robust predictions of near-term changes in the tropospheric ozone burden, and we review how progress can be made to reduce this limitation

Light-induced protein nitration and degradation with HONO emission

Proteins can be nitrated by air pollutants (NO2), enhancing their allergenic potential. This work provides insight into protein nitration and subsequent decomposition in the present of solar radiation. We also investigated light-induced formation of nitrous acid (HONO) from protein surfaces that were nitrated either online with instantaneous gas phase exposure to NO2 or offline by an efficient nitration agent (tetranitromethane, TNM). Bovine serum albumin (BSA) and ovalbumin (OVA) were used as model substances for proteins. Nitration degrees of about 1 % were derived applying NO2 concentrations of 100 ppb under VIS/UV illuminated condition, while simultaneous decomposition of (nitrated) proteins was also found during long-term (20 h) irradiation exposure. Gas exchange measurements of TNM-nitrated proteins revealed that HONO can be formed and released even without contribution of instantaneous heterogeneous NO2 conversion. However, fumigation with NO2 was found to increase HONO emissions substantially. In particular, a strong dependence of HONO emissions on light intensity, relative humidity (RH), NO2 concentrations and the applied coating thickness were found. The 20 hours long-term studies revealed sustained HONO formation, even if concentrations of the intact (nitrated) proteins were too low to be detected after the gas exchange measurements. A reaction mechanism for the NO2 conversion based on the Langmuir-Hinshelwood kinetics is proposed

Light induced uptake of NO2 on submicron humic acid aerosol

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Light Induced Uptake of NO2 on Submicron Humic Acid Aerosol

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Light induced conversion of nitrogen dioxide into nitrous acid on submicron humic acid aerosol

International audienceThe interactions of aerosols consisting of humic acids with gaseous nitrogen dioxide (NO2) were investigated under different light conditions in aerosol flow tube experiments at ambient pressure and temperature. The results show that NO2 is converted on the humic acid aerosol into nitrous acid (HONO), which is released from the aerosol and can be detected in the gas phase at the reactor exit. The formation of HONO on the humic acid aerosol is strongly activated by light: In the dark, the HONO-formation was below the detection limit, but it was increasing with the intensity of the irradiation with visible light. Under simulated atmospheric conditions with respect to the actinic flux, relative humidity and NO2-concentration, reactive uptake coefficients ?rxn for the NO2?HONO conversion on the aerosol between ?rxn -7 (in the dark) and ?rxn=6×10-6 were observed. The observed uptake coefficients decreased with increasing NO2-concentration in the range from 2.7 to 280 ppb and were dependent on the relative humidity (RH) with slightly reduced values at low humidity (60% RH). The measured uptake coefficients for the NO2?HONO conversion are too low to explain the HONO-formation rates observed near the ground in rural and urban environments by the conversion of NO2?HONO on organic aerosol surfaces, even if one would assume that all aerosols consist of humic acid only. It is concluded that the processes leading to HONO formation on the Earth surface will have a much larger impact on the HONO-formation in the lowermost layer of the troposphere than humic materials potentially occurring in airborne particles

Light induced conversion of nitrogen dioxide into nitrous acid on submicron humic acid aerosol

International audienceThe interactions of aerosols consisting of humic acids with gaseous nitrogen dioxide (NO2) were investigated under different light conditions in aerosol flow tube experiments at ambient pressure and temperature. The results show that NO2 is converted on the humic acid aerosol into nitrous acid (HONO), which is released from the aerosol and can be detected in the gas phase at the reactor exit. The formation of HONO on the humic acid aerosol is strongly activated by light: In the dark, the HONO-formation was below the detection limit, but it was increasing with the intensity of the irradiation with visible light. Under simulated atmospheric conditions with respect to the actinic flux, relative humidity and NO2-concentration, reactive uptake coefficients γrxn for the NO2→HONO conversion on the aerosol between γrxn 60% RH). The measured uptake coefficients for the NO2→HONO conversion are too low to explain the HONO-formation rates observed near the ground in rural and urban environments by the conversion of NO2→HONO on organic aerosol surfaces, even if one would assume that all aerosols consist of humic acid only. It is concluded that the processes leading to HONO formation on the Earth surface will have a much larger impact on the HONO-formation in the lowermost layer of the troposphere than humic materials potentially occurring in airborne particles

Evaluation of 1,3,5 trimethylbenzene degradation in the detailed tropospheric chemistry mechanism, MCMv3.1, using environmental chamber data

The degradation mechanism of 1,3,5-trimethyl-benzene (TMB) as implemented in the Master Chemical Mechanism version 3.1 (MCM) was evaluated using data from the environmental chamber at the Paul Scherrer Institute. The results show that the MCM provides a consistent description of the photo-oxidation of TMB/NO(x) mixtures for a range of conditions. In all cases the agreement between the measurement and the simulation decreases with decreasing VOC-NO(x) ratio and in addition with increasing precursor concentration. A significant underestimation of the decay rate of TMB and thus underestimation of reactivity in the system, consistent with results from previous appraisals of the MCM, was observed. Much higher nitrous acid (HONO) concentrations compared to simulations and expected from chamber characterization experiments were measured during these smog chamber experiments. A light induced NO(2) to HONO conversion at the chamber walls is suggested to occur. This photoenhanced NO(2) to HONO conversion with subsequent HONO photolysis enhances the reactivity of the system. After the implementation of this reaction in the model it describes the decay of TMB properly. Nevertheless, the model still overpredicts ozone at a later stage of the experiment. This can be attributed to a too slow removal of NO2. It is also shown that this photo-enhanced HONO formation is not restricted to TMB photo-oxidation but also occurs in other chemical systems (e. g. alpha-pinene). However, the influence of HONO as a source of OH radicals is less important in these more reactive systems and therefore the importance of the HONO chemistry is less obvious