Abstract
Collocated data of the moderate resolution imaging spectroradiometer (MO-DIS) Collection 6.1 aerosol optical depths (AOD) at 3 km × 3 km north of 59.9°N over ocean were assessed at 550 nm by aerosol robotic network (AERONET) data from coastal sites and marine aerosol network (MAN) data from vessels during June to October 2006 to 2018. Typically, MODIS AOD was higher at low and lower at high values than the AERONET AOD. Discrepancies were largest for sites where the Earth’s surface around the site is very heterogeneous (Canadian Archipelago, coast of Greenland). Due to the higher likelihood for sea-ice, MAN and MODIS AOD differed stronger west of Greenland and over the Beaufort Sea than at location in the Greenland and Norwegian Seas and Atlantic. MODIS AOD well captured the inter-seasonal variability found in the AERONET AOD data (R = 0.933). At all sites, MO-DIS and AERONET AOD agreement improved as time progressed in the shipping season, hinting at errors in sea-ice vs. open water classification. Overall 75.3% of the MODIS AOD data fell within the limits of the error envelops of the AERONET/MAN AOD data with MAN ranging between 87.5% and 100%. Changes in both MODIS and AERONET mean AOD between two periods of same length (2006-2011, 2013-2018) were explainable by changes in emissions for all sites.
Highlights
In the maritime Arctic, aerosols stem from both natural and anthropogenic emissions
Overall 75.3% of the moderate resolution imaging spectroradiometer (MODIS) aerosol optical depths (AOD) data fell within the limits of the error envelops of the aerosol robotic network (AERONET)/marine aerosol network (MAN) AOD data with MAN ranging between 87.5% and 100%
We looked for changes in agreement between MODIS and AERONET AOD over the time of the shipping season
Summary
In the maritime Arctic, aerosols stem from both natural and anthropogenic emissions. In winter and early spring, the so-called Arctic Haze includes both types of emissions from the advection of pollutants and aerosols emitted in mid-latitudes [1]. Natural Arctic aerosol contains more than 50% oceanic sea-salt mass fraction, 30% - 35% mineral dust, and lower fractions of non-sea-salt sulfate, methane sulfonic acid, and biomass burning products [2]. In summer and early fall, Arctic shipping releases primary aerosols and aerosol precursor gases like sulfur dioxide, nitrogen oxides and volatile organic compounds into the marine and coastal atmospheric boundary layer (ABL) [3]-[8]. Secondary pollutants and/or secondary aerosols form by chemical reactions, gas-to-particle conversion and accumulation [9]. Year-round anthropogenic emissions occur in the Arctic due to offshore oil/gas activities (e.g. flaring, traffic to/from oil-platforms) [10] [11] and Arctic communities [12]
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