Rapid new particle formation driven by methanesulfonic acid and amines

The formation and radiative properties of clouds in the marine boundary layer are highly sensitive to the number of cloud condensation nuclei (CCN), which largely originate from new particle formation. At present, most climate models only consider new particle formation from sulfuric acid (SA), in pristine marine regions produced via oxidation of dimethyl sulfide (DMS) emitted by phytoplankton. However, DMS oxidation also yields methanesulfonic acid (MSA) - often in higher amounts than SA under cool conditions (<10 °C) - yet MSA's role in NPF remains elusive. Here, we present results from the CERN CLOUD chamber at temperatures of -10 °C and +5 °C, demonstrating NPF from MSA and amines (dimethylamine, DMA, and trimethylamine, TMA). We isolated effects of MSA from SA by generating MSA from an evaporator at concentrations between 10⁵ and 10⁸ cm^-3. We find MSA and DMA form particles at +5 °C but nucleation rates (J _1.7) are slow, reaching about 1 cm^-3 s^-1 at MSA concentrations of 5 × 10⁷ cm^-3. However, in the presence of low concentrations of SA (below 10⁶ cm^-3) and 2-15 pptv DMA, MSA at few 10⁷ cm^-3 strongly enhances SA-DMA nucleation, reaching up to 80 cm^-3 s^-1. Our measurements confirm MSA together with SA and DMA molecules in initial molecular clusters during nucleation. We find TMA less effective than DMA for new particle formation, likely resulting from steric hindrance of the additional methyl group. Our findings show that MSA can boost NPF rates by 1-2 orders of magnitude in pristine marine environments and should be incorporated in climate models.