Changes in Atmospheric Constituents and in Radiative Forcing

The present paper reviews existing knowledge with regard to Organic Aerosol (OA) of importance for global climate modelling and defines critical gaps needed to reduce the involved uncertainties. All pieces required for the representation of OA in a global climate model are sketched out with special attention to Secondary Organic Aerosol (SOA): The emission estimates of primary carbonaceous particles and SOA precursor gases are summarized. The up-to-date understanding of the chemical formation and transformation of condensable organic material is outlined. Knowledge on the hygroscopicity of OA and measurements of optical properties of the organic aerosol constituents are summarized. The mechanisms of interactions of OA with clouds and dry and wet removal processes parameterisations in global models are outlined. This information is synthesized to provide a continuous analysis of the flow from the emitted material to the atmosphere up to the point of the climate impact of the produced organic aerosol. The sources of uncertainties at each step of this process are highlighted as areas that require further studies.

/pdf/organic-aerosol-and-global-climate-modelling-a-review-4ojfzx6x50.pdf

Organic aerosol and global climate modelling: a review

. The Model for Ozone and Related chemical Tracers, version 4 (MOZART-4) is an offline global chemical transport model particularly suited for studies of the troposphere. The updates of the model from its previous version MOZART-2 are described, including an expansion of the chemical mechanism to include more detailed hydrocarbon chemistry and bulk aerosols. Online calculations of a number of processes, such as dry deposition, emissions of isoprene and monoterpenes and photolysis frequencies, are now included. Results from an eight-year simulation (2000–2007) are presented and evaluated. The MOZART-4 source code and standard input files are available for download from the NCAR Community Data Portal ( http://cdp.ucar.edu ).

/pdf/description-and-evaluation-of-the-model-for-ozone-and-31ritydpb8.pdf

Description and evaluation of the Model for Ozone and Related chemical Tracers, version 4 (MOZART-4)

In the spring of 1988 an interagency consortium of Federal Land Managers and the Environmental Protection Agency initiated a national visibility and aerosol monitoring network to track spatial and temporal trends of visibility and visibility-reducing particles. The monitoring network consists of 36 stations located mostly in the western United States. The major visibility-reducing aerosol species, sulfates, nitrates, organics, light-absorbing carbon, and wind-blown dust are monitored as well as light scattering and extinction. Sulfates and organics are responsible for most of the extinction at most locations throughout the United States, while at sites in southern California nitrates are dominant. In the eastern United States, sulfates contribute to about two thirds of the extinction. In almost all cases, extinction and the major aerosol types are highest in the summer and lowest during the winter months.

Spatial and seasonal trends in particle concentration and optical extinction in the United States

A computationally efficient and rigorous thermodynamic model that predicts the physical state and composition of inorganic atmospheric aerosol is presented. One of the main features of the model is the implementation of mutual deliquescence of multicomponent salt particles, which lowers the deliquescence point of the aerosol phase. The model is used to examine the behavior of four types of tropospheric aerosol (marine, urban, remote continental and non-urban continental), and the results are compared with the predictions of two other models currently in use. The results of all three models were generally in good agreement. Differences were found primarily in the mutual deliquescence humidity regions, where the new model predicted the existence of water, and the other two did not. Differences in the behavior (speciation and water absorbing properties) between the aerosol types are pointed out. The new model also needed considerably less CPU time, and always shows stability and robust convergence.

http://nenes.eas.gatech.edu/Reprints/ISORROPIA_AG.pdf

ISORROPIA: A New Thermodynamic Equilibrium Model for Multiphase Multicomponent Inorganic Aerosols

Water activities, densities, and refractive indices over extended concentration ranges at 25{degrees}C are reported for solution droplets containing a single salt of either (NH{sub 4}){sub 2}SO{sub 4}, NH{sub 4}HSO{sub 4}, (NH{sub 4}){sub 3}H(SO{sub 4}){sub 2}, Na{sub 2}SO{sub 4}, NaHSO{sub 4}, or NaNO{sub 3}, which are common constituents of atmospheric aerosols. The extensive data reported are obtained from experiments using the single-particle levitation technique recently developed for measuring the thermodynamic and optical properties of microdroplets. These data should find application in mathematical models predicting the dynamic behavior, visibility reduction, and radiative effects of atmospheric sulfate and nitrate aerosols. 32 refs., 13 figs., 3 tabs.

I.N. Tang

Papers

Water activities, densities, and refractive indices of aqueous sulfates and sodium nitrate droplets of atmospheric importance

Composition and temperature dependence of the deliquescence properties of hygroscopic aerosols

The relative importance of atmospheric sulfates and nitrates in visibility reduction

Aerosol growth studies — IV. Phase transformation of mixed salt aerosols in a moist atmosphere

On the equilibrium partial pressures of nitric acid and ammonia in the atmosphere