An advanced modelling study on the role of dimethyl sulfide in new particle formation in the pristine marine boundary layer

Abstract

New particle formation (NPF) enhances the concentration of cloud condensation nuclei (CCN) over the oceans, thereby affecting the radiative balance and, consequently, Earth's climate. The literature suggest that marine NPF predominantly occurs in the free troposphere, as the extensive surface area of sea spray aerosols and limited precursor gases suppress NPF in the marine boundary layer (MBL). However, such interpretations do not fully account for the observations on nucleation and Aitken-mode particles within the MBL. Here, we demonstrate how natural emissions of dimethyl sulfide (DMS) and NH 3 can drive H 2 SO 4 –NH 3 -derived NPF in the MBL during cloud-free conditions following precipitation events. The newly formed particles manage to grow into the upper Aitken and accumulation mode size range within 3–4 d, with the potential to act as CCN. Through extensive sensitivity runs, we show that DMS-derived NPF and growth exhibits a non-linear response to variations in air temperature and wind speed, whereas their response to changes in sea surface temperature, precipitation rate, and DMS surface ocean concentration remains approximately linear. Sporadic cloud cover is shown to suppress NPF. Finally, we employ quantum chemical calculations to provide temperature dependant rate coefficients for the OH-initiated oxidation of methane sulphinic acid (MSIA). We also assess other key uncertainties in the DMS oxidation mechanism to illustrate their impact on the formation and growth of DMS-derived aerosol particles in the MBL.