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R. Wolke et al.
60.1 Introduction
The tropospheric chemistry is strongly influenced by the budget of nitrogen oxides
(NO x ). The chemical mechanisms controlling this budget have also a large impact
on ozone and the oxidizing capacity of the atmosphere. At day-time, nitrogen oxides
are mainly removed from the atmosphere by the formation of nitric acid (HNO 3 )
via the reaction of NO 2 and OH. During night-time, the heterogeneous hydrolysis
of N 2 O 5 on the surface of deliquescent aerosol particles represents a major source
for HNO 3 and acts as an important sink of NO x in the atmosphere. The heterogeneous N 2 O 5 hydrolysis was incorporated in global and regional chemistry transport
models and its impact on atmospheric chemistry was investigated in several studies
[4, 5, 10]. Usually, the heterogeneous N 2 O 5 hydrolysis is implemented into chemical
transport models as a first-order loss reaction.
N 2 O 5
(aerosol)
→ 2HNO 3
(60.1)
with a rate constant k N 2 O 5 . In the originally version of COSMO-MUSCAT [17] this
constant is calculated by an approach of [3] which depends only from the relative
humidity (RH). Aiming to advance the representativeness of heterogeneous hydrolysis of N 2 O 5 , we propose a new parameterization depending on temperature, RH, and
particle composition [5]. The influence of surface area concentration on the hydrolysis rate is also comprehensively considered. This new scheme was implemented in
the model system COSMO-MUSCAT in order to investigate the impact of heterogeneous hydrolysis of N 2 O 5 on the particulate nitrate formation. The model simulations
were performed for different configurations and the period from March to November
2010. The results were compared and evaluated by filter measurements in Melpitz
and two other Germany sites (Neuglobsow, Waldhof; www.umweltbundesamt.de).
60.2 Model Framework
Chemistry-transport model. COSMO-MUSCAT is a state-of-the-art multiscale
model system developed by the modelling department of TROPOS, which is qualified for process studies in local and regional areas. The model system comprises the
numerical weather forecast model of the German Weather Service (DWD) COSMO
[11] and the chemistry transport model MUSCAT [17]. The model was applied to
different investigations, e.g. air quality studies treating local as well as regional areas
[7, 15]. Driven by the meteorological model, MUSCAT treats the atmospheric transport as well as chemical transformations for several gas phase species and particle
populations. The transport processes include advection, turbulent diffusion, sedimentation, dry and wet deposition. In this study, the gas-phase reaction system is
described by the chemical mechanism RACM-MIM2 [8, 16], which consists of 87
species and more than 200 reactions. The aerosol processes are represented by a
mass-based approach.
R. Wolke et al.
60.1 Introduction
The tropospheric chemistry is strongly influenced by the budget of nitrogen oxides
(NO x ). The chemical mechanisms controlling this budget have also a large impact
on ozone and the oxidizing capacity of the atmosphere. At day-time, nitrogen oxides
are mainly removed from the atmosphere by the formation of nitric acid (HNO 3 )
via the reaction of NO 2 and OH. During night-time, the heterogeneous hydrolysis
of N 2 O 5 on the surface of deliquescent aerosol particles represents a major source
for HNO 3 and acts as an important sink of NO x in the atmosphere. The heterogeneous N 2 O 5 hydrolysis was incorporated in global and regional chemistry transport
models and its impact on atmospheric chemistry was investigated in several studies
[4, 5, 10]. Usually, the heterogeneous N 2 O 5 hydrolysis is implemented into chemical
transport models as a first-order loss reaction.
N 2 O 5
(aerosol)
→ 2HNO 3
(60.1)
with a rate constant k N 2 O 5 . In the originally version of COSMO-MUSCAT [17] this
constant is calculated by an approach of [3] which depends only from the relative
humidity (RH). Aiming to advance the representativeness of heterogeneous hydrolysis of N 2 O 5 , we propose a new parameterization depending on temperature, RH, and
particle composition [5]. The influence of surface area concentration on the hydrolysis rate is also comprehensively considered. This new scheme was implemented in
the model system COSMO-MUSCAT in order to investigate the impact of heterogeneous hydrolysis of N 2 O 5 on the particulate nitrate formation. The model simulations
were performed for different configurations and the period from March to November
2010. The results were compared and evaluated by filter measurements in Melpitz
and two other Germany sites (Neuglobsow, Waldhof; www.umweltbundesamt.de).
60.2 Model Framework
Chemistry-transport model. COSMO-MUSCAT is a state-of-the-art multiscale
model system developed by the modelling department of TROPOS, which is qualified for process studies in local and regional areas. The model system comprises the
numerical weather forecast model of the German Weather Service (DWD) COSMO
[11] and the chemistry transport model MUSCAT [17]. The model was applied to
different investigations, e.g. air quality studies treating local as well as regional areas
[7, 15]. Driven by the meteorological model, MUSCAT treats the atmospheric transport as well as chemical transformations for several gas phase species and particle
populations. The transport processes include advection, turbulent diffusion, sedimentation, dry and wet deposition. In this study, the gas-phase reaction system is
described by the chemical mechanism RACM-MIM2 [8, 16], which consists of 87
species and more than 200 reactions. The aerosol processes are represented by a
mass-based approach.