A global off-line model of size-resolved aerosol microphysics: I. Model development and prediction of aerosol properties

Abstract

Abstract.A GLObal Model of Aerosol Processes (GLOMAP) has been developed as an extension to the TOMCAT 3-D Eulerian off-line chemical transport model. GLOMAP simulates the evolution of the global aerosol size distribution using a sectional two-moment scheme and includes the processes of aerosol nucleation, condensation, growth, coagulation, wet and dry deposition and cloud processing. We describe the results of a global simulation of sulfuric acid and sea spray aerosol. The model captures features of the aerosol size distribution that are well established from observations in the marine boundary layer and free troposphere. Modelled condensation nuclei (CN >3 nm) vary between about 250-500 cm −3 in remote marine boundary layer regions and are generally in good agreement with observations. Modelled continental CN concentrations are lower than observed, which may be due to lack of some primary aerosol sources or the neglect of nucleation mechanisms other than binary homogeneous nucleation of sulfuric acidwater particles. Remote marine CN concentrations increase to around 2000-10 000 cm −3 (at standard temperature and pressure) in the upper troposphere, which agrees with typical observed vertical profiles. Cloud condensation nuclei (CCN) at 0.2% supersaturation vary between about 1000 cm −3 in polluted regions and between 10 and 500 cm −3 in the remote marine boundary layer. New particle formation through sulfuric acid-water binary nucleation occurs predominantly in the upper troposphere, but the model results show that these particles contribute greatly to aerosol concentrations in the marine boundary layer. For this sulfur-sea salt system it is estimated that sea spray emissions account for only ∼10% of CCN in the tropical marine boundary layer, but between 20 and 75% in the mid-latitude Southern Ocean. In a run with only natural sulfate and sea salt emissions the global mean surface CN concentration is more than 60% of that from a run Correspondence to: D. V. Spracklen (dominick@env.leeds.ac.uk) with 1985 anthropogenic sulfur emissions, although the natural emissions comprise only 27% of total sulfur emissions. Southern hemisphere marine boundary layer CN are more than 90% natural in origin, while polluted continental CN are more than 90% anthropogenic in origin, although these numbers will change when other anthropogenic CN sources are included in the model.

Aerosol microphysics simulations of the Mt.~Pinatubo eruption with the UM-UKCA composition-climate model

“…The GLOMAP aerosol microphysics module was initially developed as a component of the TOMCAT 3-D offline Chemical Transport Model (Chipperfield, 2006) with both 2-moment sectional (Spracklen et al, 2005) and 2-moment modal versions (Mann et al, 2010) available. The computationally faster modal scheme (GLOMAP-mode) was specifically designed for longer integrations within UM-UKCA and applies the same aerosol microphysics representations as the sectional scheme but with the size distribution parameterised into seven log-normal modes, being similar in framework to that used in ECHAM-HAM (e.g.…”

Cloud condensation nuclei over the Southern Ocean: wind dependence and seasonal cycles

“…There can be little doubt that global numerical models that include realistic aerosol microphysical processes, coupled with accurate data on aerosol and precursors, are the best tools to understand future aerosol impacts on climate, as attested by developments such as Spracklen et al (2005), Pierce and Adams (2006), Korhonen et al (2008), Wang et al (2009), Mann et al (2010) and Lee et al (2015). Whilst one significant component in the building of confidence in such models is the availability of representative climatologies of aerosol properties, such as cloud condensation nucleus (CCN) concentration on a global scale, information on the range of aerosol properties on this scale, certainly from in situ observations, is always likely to be relatively limited.…”

Fast retrievals of tropospheric carbonyl sulfide with IASI

“…These are also areas of known SO 2 emissions due to industrial processes and energy production that are routinely modelled in chemical transport models, such as TOMCAT (Spracklen et al, 2005). While it is energetically unfavourable for SO 2 to convert to OCS, the two may be positively correlated in many physical situations, especially in anthropogenic processes that do not have strict methods in place to reduce SO 2 emissions.…”