A Lagrangian particle model with chemical reactions: application in real atmosphere

Abstract

Abstract:In this work a lagrangian particle model able to account for simple chemical reactions between NO and O 3 (Alessandrini et al., 2007) has been improved in order to consider the photolysis of NO 2 . A system of chemical equations is numerically solved on an eulerian grid, while the particles trajectories are moved in a lagrangian frame. The NOx emissions of a power plant in real atmosphere, situated in a complex topography environment, have been considered as a test case. The meteorological model RAMS has been applied to build the wind field together with the interface code MIRS to compute turbulence parameters, requested for the dispersion simulations. The plume transitions over an air quality station, allowing for a comparison between the measured and computed concentrations of all the reaction's compounds (NO, NO 2 and O 3 ), have been simulated by the lagrangian particle model. The simulated episodes refer to the diurnal time, when the ultraviolet radiation activates the NO 2 photolysis making necessary the model complete set of chemical equations. In order to reduce computational cost and improve the accuracy of the background O 3 concentration representation, the concept of concentration deficit carried by the particles is proposed and tested. This new method does not need to release a big amount of particles filling the whole domain, but only the inside plume particles should be accounted for. Comparisons between NO/NO 2 's concentrations ratio are presented in term of scatter plots and statistical indexes analysis. The satisfactory results suggest that the model can be used in practical applications in real atmosphere also for regulatory purposes when the NO 2 concentration limits are imposed by the legislation.Key words: Atmospheric dispersion, NO, chemistry model, Lagrangian Particle Model, photo-stationary equilibrium. INTRODUCTIONThe chemical reactions of the pollutants released by a source with the background ambient chemical compounds are a very important task for the air quality and regulatory models; for example when dealing with NO x source and the related photochemical pollution. This aim is generally achieved in the frame of the Eulerian models by considering very complicated chemical schemes, including a large set of reactions and assuming the times scale for turbulence and chemistry such that to allow equilibrium hypothesis (Jacobson, 2001, Griffin et al., 2002, Sokhi et al., 2006. In this way the segregation due to the correlation between the concentration of the chemical compounds is neglected and it is not needed a turbulent model providing these terms. However, in many pollution phenomena, when the time and spatial scales are small, as for example close to the source or in urban environment, this assumption cannot be made and non equilibrium must be considered in order to avoid a too fast reaction rate. The covariance of the concentration should also be known if one had to simulate chemical reactions at small temporal and spatial scales, where the chemical equilibrium is not ye...

A stochastic Lagrangian micromixing model for the dispersion of reactive scalars in turbulent flows: role of concentration fluctuations and improvements to the conserved scalar theory under non-homogeneous conditions

“…The state-of-the-art Lagrangian stochastic model (Thomson, 1987, [63]) coupled with the chemical scheme of Alessandrini & Ferrero (2009, [3]; 2011, [2]) is here used to provide unpublished results, which are used for inter-comparison purposes (Sec.3.11). At each time step, this model updates the particle position using a stochastic model equation, then the concentrations of each substance is calculated over a static Eulerian grid.…”

Impact Assessment of Pollutant Emissions in the Atmosphere from a Power Plant over a Complex Terrain and under Unsteady Winds

“…Lagrangian models are the used to properly simulate the pollutant dispersion in a complex terrain [14,15,17,[19][20][21]: SPRAY does not include atmospheric photochemical processes, and only few models coupling Lagrangian dispersion with atmospheric chemistry exist in the literature of [32][33][34]. This study aimed to assess the impact of NO x stack emissions on local air quality: since regulatory emission limits for combustion plants are set for NO x (2010/75/UE), while for air quality are set for NO 2 (2008/50/EC), the simulation of NO x dispersion represents a conservative and precautionary approach, since NO x includes both NO 2 and NO.…”

“…Considering the annual air quality reports for the simulation domain [32,33], it was possible to characterize the summer and the fall periods to be investigated.…”

Atmospheric Pollutant Dispersion over Complex Terrain: Challenges and Needs for Improving Air Quality Measurements and Modeling

“…First [224] and second order [225][226][227][228][229][230] chemical reactions can be solved in Lagrangian models, but only a limited number of chemical equations can be taken into account. It is generally recognized that the segregation of the chemical reactants cannot be neglected in short-term concentration predictions [231] when chemical reactions take place before the pollutants are well mixed by the turbulence.…”