Search

Byline: J. Bednar, J. Brechler, T. Halenka A model for simulation and evaluation of summer episodes of anthropogenic surface ozone (summer smog episodes) is presented in this paper. This model has been used for air-pollution studies in the region of Prague (central part of Bohemia, the Czech Republic). It is based on so-called 'puff model' technology and the Lagrangian method of trajectory construction in the boundary layer of the atmosphere is applied. Processes of turbulent dispersion of puffs, photochemical and other chemical transformations and deposition of compounds on the Earth's surface are also taken into account. A brief informative presentation of model results is included.

For the purpose of qualifying and quantifying the impact of urban emission from Central European cities on the present-day regional air-quality, the regional climate model RegCM4.2 was coupled with the chemistry transport model CAMx, including two-way interactions. A series of simulations was carried out for the 2001-2010 period either with all urban emissions included (base case) or without considering urban emissions. Further, the sensitivity of ozone production to urban emissions was examined by performing reduction experiments with 20% emission perturbation of NOx and/or NMVOC. The validation of the modeling system's air-quality related outputs using AirBase and EMEP surface measurements showed satisfactory reproduction of the monthly variation for ozone (O3), nitrogen dioxide (NO2) and sulfur dioxide (SO2). In terms of hourly correlations, reasonable values are achieved for ozone (r around 0.5-0.8) and for NO2 (0.4-0.6), but SO2 is poorly or not correlated at all with measurements (r around 0.2- 15 0.5). The modeled fine particulates (PM2.5) are usually underestimated, especially in winter, mainly due to underestimation of nitrates and carbonaceous aerosols. EC air-quality measures were chosen as metrics describing the cities emission impact on regional air pollution. Due to urban emissions, significant ozone titration occurs over cities while over rural areas remote from cities, ozone production is modeled, mainly in terms of number of exceedances and accumulated exceedances over the threshold of 40 ppbv. Urban NOx, SO2 and PM2.5 emissions also significantly contribute to concentrations in the cities themselves (up to 50-70% for NOx and SO2, and up to 60% for PM2.5), but the contribution is large over rural areas as well (10-20%). Although air pollution over cities is largely determined by the local urban emissions, considerable (often a few tens of %) fraction of the concentration is attributable to other sources from rural areas and minor cities. Further, for the case of Prague (Czech Republic capital) it is shown that the inter-urban interference between large cities does not play an important role which means that the impact on a chosen city of emissions from all other large cities is very small. The emissions perturbation experiments showed that to achieve significant ozone reduction over cities in central Europe, the emission control strategies have to focus on the reduction of NMVOC, as reducing NOx, due to suppressed titration, leads often to increased O3. The influence over rural areas remote from cities is however always in favor of improved air-quality, i.e. both NOx and/or NMVOC reduction ends up in decreased ozone pollution, mainly in terms of exceedances. [ABSTRACT FROM AUTHOR]

In general, regional and global chemistry transport models apply instantaneous mixing of emissions into the model's finest resolved scale. In case of a concentrated source, this could result in erroneous calculation of the evolution of both primary and secondary chemical species. Several studies discussed this issue in connection with emissions from ships and aircraft. In this study, we present an approach to deal with the non-linear effects during dispersion of NOx emissions from ships. It represents an adaptation of the original approach developed for aircraft NOx emissions, which uses an exhaust tracer to trace the amount of the emitted species in the plume and applies an effective reaction rate for the ozone production/destruction during the plume's dilution into the background air. In accordance with previous studies examining the impact of international shipping on the composition of the troposphere, we found that the contribution of ship induced surface NOx to the total reaches 90% over remote ocean and makes 10-30% near coastal regions. Due to ship emissions, surface ozone increases by up to 4- 6 ppbv making 10% contribution to the surface ozone budget. When applying the ship plume parameterization, we show that the large scale NOx decreases and the ship NOx contribution is reduced by up to 20-25%. A similar decrease was found in the case of O3. The plume parameterization suppressed the ship induced ozone production by 15-30% over large areas of the studied region. To evaluate the presented parameterization, nitrogen monoxide measurements over the English Channel were compared with modeled values and it was found that after activating the parameterization the model accuracy increases. [ABSTRACT FROM AUTHOR]

In general, regional and global chemistry transport models apply instantaneous mixing of emissions into the model's finest resolved scale. In case of a concentrated source, this could result in erroneous calculation of the evolution of both primary and secondary chemical species. Several studies discussed this issue in connection with emissions from ships and aircrafts. In this study, we present an approach to deal with the non-linear effects during dispersion of NOx emissions from ships. It represents an adaptation of the original approach developed for aircraft NOx emissions, which uses an exhaust tracer to trace the amount of the emitted species in the plume and applies an effective reaction rate for the ozone production/destruction during the plume's dilution into the background air. In accordance with previous studies examining the impact of international shipping on the composition of the troposphere, we found that the contribution of ship induced surface NOx to the total reaches 90% over remote ocean and makes 10-30% near coastal regions. Due to ship emissions, surface ozone increases by up to 4-6 ppbv making 10% contribution to the surface ozone budget. When applying the ship plume parameterization, we showed that the large scale NOx decreases and the ship NOx contribution is reduced by up to 20-25%. Similar decrease was found in case of O3. The plume parameterization suppressed the ship induced ozone production by 15-30% over large areas of the focused region. To evaluate the presented parameterization, nitrogen oxide measurements over the English Channel were compared with modeled values and it was found that after activating the parameterization the model accuracy increases. [ABSTRACT FROM AUTHOR]

Regional air quality decadal simulations were carried out using the air quality model CAMx driven off-line by the regional climate model RegCM3 for the time slice 1991- 2000 using two different datasets of external meteorological forcing to constrain RegCM3: the ERA40 global atmospheric reanalysis dataset and the output from the GCM ECHAM5. The focus of this work is to compare the perfect lateral boundary conditions experiment with the GCM driven control experiment and to investigate how this external meteorological forcing affects near surface ozone. The different RegCM3 meteorological forcings resulted in changes of near surface ozone over Europe ranging between ±5 ppb for winter and summer, while all model parameterizations and anthropogenic emissions remained unchanged. Changes in near surface ozone are induced by changes in meteorological fields and biogenic emissions, which are on-line calculated and meteorology-dependent. The model simulations suggest that the change in solar radiation is the factor that mostly modulates the ozone changes in summer. During winter season it is found that the induced changes in NOx explain about 40% of the ozone variability. The meteorological induced changes in biogenic emissions are quite low for winter with rather small impact on ozone while they are more temperature than radiation dependent. Using multiple regression analysis to associate the changes in near surface ozone with the respective changes in selected meteorological parameters and ozone precursors, an explained variance of 70% in summer and 60% in winter is reproduced. [ABSTRACT FROM AUTHOR]