Size-resolved characteristics of water-soluble particulate elements in a coastal area: Source identification, influence of wildfires, and diurnal variability

Size-resolved elemental measurements were conducted for the water-soluble fraction of particulate matter at a central California coastal city, Marina, during two separate summertime field campaigns: the Nucleation in California Experiment (NiCE) in 2013 and the Fog and Stratocumulus Evolution (FASE) campaign in 2016. Two Micro-Orifice Uniform Deposit Impactors (MOUDIs) were used to quantify mass size distributions of 29 elements and a Positive Matrix Factorization (PMF) model revealed six characteristic sources during the measurement periods: (i) Crustal Emissions (3.9% of total mass), (ii) Secondary Aerosol (24.4%), (iii) Biomass Burning (13.1%), (iv) Waste Facilities (8.7%), (v) Vehicular Emissions (4.4%), and (vi) Marine Emissions (45.4%). Characteristic elements from each of these sources included the following: (i) Crustal Emissions (Fe, Al, Ti, Pt), (ii) Secondary Aerosol (Zn, As, Rb, K, Cu, V), (iii) Biomass Burning (Rb, K, Cu, Pt), (iv) Waste Facilities (Ag, Cd, Ni, Al), (v) Vehicular Emissions (Zn, Zr, V, Mn), and (vi) Marine Emissions (Na, Sr, V, Mn). Temporally-resolved results revealed higher PM levels associated with Vehicular Emissions (day/night mass concentration ratio = 31.3), Crustal Emissions (day/night = 20.0), and Secondary Aerosol (day/night = 27.2) during the day compared to night due to some combination of more daytime anthropogenic activity, wind speed/directional factors, and photochemistry. The Marine Emissions factor exhibited a day/night concentration ratio of exactly 1.0. Mass size distributions revealed characteristic peaks in four diameter ranges: 0.1–0.18 μm, 0.32–0.56 μm, 1.0–1.8 μm, and 3.2–5.6 μm. The number of modes varied depending on the species and degree of wildfire influence, with additional differences observed between the NiCE and FASE wildfire periods.