Abstract
Aerosols play an important yet uncertain role in modulating the radiation balance of the sensitive Arctic atmosphere. Organic aerosol is one of the most abundant, yet least understood, fractions of the Arctic aerosol mass. Here we use data from eight observatories that represent the entire Arctic to reveal the annual cycles in anthropogenic and biogenic sources of organic aerosol. We show that during winter, the organic aerosol in the Arctic is dominated by anthropogenic emissions, mainly from Eurasia, which consist of both direct combustion emissions and long-range transported, aged pollution. In summer, the decreasing anthropogenic pollution is replaced by natural emissions. These include marine secondary, biogenic secondary and primary biological emissions, which have the potential to be important to Arctic climate by modifying the cloud condensation nuclei properties and acting as ice-nucleating particles. Their source strength or atmospheric processing is sensitive to nutrient availability, solar radiation, temperature and snow cover. Our results provide a comprehensive understanding of the current pan-Arctic organic aerosol, which can be used to support modelling efforts that aim to quantify the climate impacts of emissions in this sensitive region.
Highlights
Organic aerosols (OAs) contribute to the Arctic aerosol mass near the surface[1–4] and affect the local climate through direct aerosol–radiation interactions and by altering the cloud properties[5,6]
Of 16 models deployed in a recent AeroCom evaluation of the simulated annual aerosol optical depth in Polar Regions[32], only 6 considered biogenic precursors, which can contribute to particle growth and so the size range of cloud condensation nuclei
We found West Siberian locations (Fig. 4) as a major potential source region of the primary-anthropogenic organic aerosol (POA) in winter, similar to those previously found for surface black carbon[42,60,61]
Summary
OA (ng m–3) TIK 1,380 PAL 220 PAL 950 BAR 480 BAR 330 GRU 240 UTQ UTQ 200 VRS 170 VRS 180 ALT 140 ALT ZEP ZEP. BSOA exhibits a clear annual cycle with enhanced values in June–September (Fig. 3), consistent with the exponential increase of biogenic precursor emissions with temperature[66] (Supplementary Fig. 14) This factor dominates at PAL and TIK where it contributes, on average, 40% to the total OA in the summer (Fig. 1d, Q1–Q3 = 25–53%). We found an overall nearly equal yearly abundance (Fig. 5) of summed anthropogenic-dominated OAs (average of 115 ng m−3, Q1–Q3 = 20–100 ng m−3; 95th percentile, 435 ng m−3) and summed natural-dominated OAs (average of 140 ng m−3, Q1–Q3 = 40–160 ng m−3; 95th percentile, 445 ng m−3) This indicates that the typically lower total aerosol volume/mass in the summer versus winter or spring[77] is due to species other than the total OA, which exhibits less of a seasonal cycle across the Arctic (Supplementary Fig. 16). Online content Any methods, additional references, Nature Research reporting summaries, source data, extended data, supplementary information, acknowledgements, peer review information; details of author contributions and competing interests; and statements of data and code availability are available at https://doi.org/10.1038/ s41561-021-00891-1
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