Growth of nucleation mode particles in the summertime Arctic: a case study

Megan D Willis,Jennie L Thomas,Heiko Bozem,Peter M Hoor,Jonathan P D Abbatt,W Richard Leaitch,Andreas B Herber,Amir A Aliabadi,Julia Burkart,Johannes Schneider,Franziska Köllner,Hannes Schulz

doi:10.5194/acp-16-7663-2016

Abstract

Abstract. The summertime Arctic lower troposphere is a relatively pristine background aerosol environment dominated by nucleation and Aitken mode particles. Understanding the mechanisms that control the formation and growth of aerosol is crucial for our ability to predict cloud properties and therefore radiative balance and climate. We present an analysis of an aerosol growth event observed in the Canadian Arctic Archipelago during summer as part of the NETCARE project. Under stable and clean atmospheric conditions, with low inversion heights, carbon monoxide less than 80 ppbv, and black carbon less than 5 ng m−3, we observe growth of small particles, < 20 nm in diameter, into sizes above 50 nm. Aerosol growth was correlated with the presence of organic species, trimethylamine, and methanesulfonic acid (MSA) in particles ∼ 80 nm and larger, where the organics are similar to those previously observed in marine settings. MSA-to-sulfate ratios as high as 0.15 were observed during aerosol growth, suggesting an important marine influence. The organic-rich aerosol contributes significantly to particles active as cloud condensation nuclei (CCN, supersaturation = 0.6 %), which are elevated in concentration during aerosol growth above background levels of ∼ 100 to ∼ 220 cm−3. Results from this case study highlight the potential importance of secondary organic aerosol formation and its role in growing nucleation mode aerosol into CCN-active sizes in this remote marine environment.

Highlights

In the warming Arctic (Jeffries and Richter-Menge, 2012), decreasing sea ice extent (Lindsay et al, 2009) is likely to increase the oceanic influence on atmospheric composition
In this case study we focus on the flight conducted on 12 July 2014 where Polar 6 travelled at ∼ 3 km altitude from Resolute Bay, past the marginal ice zone and out over open water to the eastern end of Lancaster Sound (Fig. 2a) as far as was permitted by our aircraft range, at which point it descended and returned west
We present evidence that growth of nucleation mode particles in the summertime Arctic can be mediated by the condensation of methanesulfonic acid (MSA) and condensible organic species

Summary

Introduction

In the warming Arctic (Jeffries and Richter-Menge, 2012), decreasing sea ice extent (Lindsay et al, 2009) is likely to increase the oceanic influence on atmospheric composition. Efficient wet removal of aerosol and less efficient transport from lower latitudes come together to suppress the condensation sink (Stohl, 2006; Engvall et al, 2008) and allow nucleation and Aitken mode particles to dominate the size distribution (Engvall et al, 2008; Heintzenberg and Leck, 2012; Croft et al, 2016) Under these clean conditions, cloud condensation nuclei (CCN) and cloud droplet number concentrations can be exceptionally low (Mauritsen et al, 2011; Leaitch et al, 2016), making summertime liquid clouds very sensitive to the formation of new particles and their growth into CCN sizes. Since Arctic clouds are an important determinant of the local surface energy balance (e.g., Intrieri et al, 2002; Lubin and Vogelmann, 2006) and have the ability to influence the thickness, freezing, and melting of sea ice (Kay and Gettelman, 2009; Tjernström et al, 2015), a predictive understanding of the sources and processes controlling CCN-active aerosol is a crucial aspect of understanding the Arctic climate

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Conclusion