Identification of Sub-micrometer Ambient Sea Salt Number Size Distribution by Positive Matrix Factorization

Sea salt aerosol is the largest natural aerosol source. The particle number size distribution (PNSD) of sea salt aerosol determines its direct and indirect radiative forcing. The PNSD of sea salt is important in quantifying the contribution of sea salt to marine cloud nuclei population. However, measuring the PNSD of sea salt is challenging, especially for sub-micrometer particles. In this study, we propose an approach to determine the PNSD of sea salt by applying positive matrix factorization (PMF) on ambient particle number size distribution data. Using the bulk PM₁ (particulate matter smaller than 1 μm in diameter) sea salt mass concentration as an external constraint, the PNSD of sea salt can be successfully retrieved. This approach is expected to advance our understanding of the global distribution and climate impact of sea salt aerosol.