Abstract
Abstract. Aerosol loading in the marine environment is investigated using aerosol composition measurements from several research ship campaigns (ICEALOT, MAP, RHaMBLe, VOCALS and OOMPH), observations of total AOD column from satellite (MODIS) and ship-based instruments (Maritime Aerosol Network, MAN), and a global chemical transport model (GEOS-Chem). This work represents the most comprehensive evaluation of oceanic OM emission inventories to date, by employing aerosol composition measurements obtained from campaigns with wide spatial and temporal coverage. The model underestimates AOD over the remote ocean on average by 0.02 (21 %), compared to satellite observations, but provides an unbiased simulation of ground-based Maritime Aerosol Network (MAN) observations. Comparison with cruise data demonstrates that the GEOS-Chem simulation of marine sulfate, with the mean observed values ranging between 0.22 μg m−3 and 1.34 μg m−3, is generally unbiased, however surface organic matter (OM) concentrations, with the mean observed concentrations between 0.07 μg m−3 and 0.77 μg m−3, are underestimated by a factor of 2–5 for the standard model run. Addition of a sub-micron marine OM source of approximately 9 TgC yr−1 brings the model into agreement with the ship-based measurements, however this additional OM source does not explain the model underestimate of marine AOD. The model underestimate of marine AOD is therefore likely the result of a combination of satellite retrieval bias and a missing marine aerosol source (which exhibits a different spatial pattern than existing aerosol in the model).
Highlights
The marine environment is generally associated with limited anthropogenic influence and clean conditions, the oceans are a major source of natural aerosols to the atmosphere, including sea salt and sulfate
This work represents the most comprehensive evaluation of oceanic organic carbon emission inventories to date, by employing aerosol composition measurements obtained from campaigns with wide spatial and temporal coverage
We find that a marine organic matter (OM) source of 8– 9 TgC yr−1 as suggested by both Spracklen et al (2008) and Langmann et al (2008), is more than sufficient to account for observed marine OM concentrations, in agreement with the lower end of the range of marine OM source estimates in the literature
Summary
The marine environment is generally associated with limited anthropogenic influence and clean conditions, the oceans are a major source of natural aerosols to the atmosphere, including sea salt and sulfate. Recent estimates of OM from marine sources range between 2.3 to 75 TgC yr−1 (Spracklen et al, 2008; Roelofs, 2008; Langmann et al, 2008; Gantt et al, 2009; Ito and Kawamiya, 2010; Myriokefalitakis et al, 2010; Long et al, 2011; Vignati et al, 2010) This wide range reflects challenges and large uncertainties associated with quantifying these emissions, as well as differences in treatment (including both sub-micron and super-micron size ranges or primary and secondary sources). In this work we apply two approaches for modeling the marine sub-micron OM source and compare those with aerosol composition measurements from several ship-based campaigns
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