Impact of wildfires on size-resolved aerosol composition at a coastal California site

Abstract

Species other than K are more reliable biomass burning tracers in region. Sulfate and nitrate peak concentrations shift to larger sizes in wildfire periods. Chloride depletion due to high levels of acidic species during wildfire periods. Soil species levels (e.g., Si, Fe, V) were enhanced during wildfires. CCN composition is dominated by ammonium during wildfire periods. Size-resolved aerosol composition measurements were conducted at a coastal site in central California during the Nucleation in California Experiment (NiCE) between July and August of 2013. The site is just east of ship and marine emission sources and is also influenced by continental pollution and wildfires, such as those near the CaliforniaeOregon border which occurred near the end of NiCE. Two micro-orifice uniform deposit impactors (MOUDIs) were used, and water-soluble and elemental compositions were measured. The five most abundant water-soluble species (in decreasing order) were chloride, sodium, non-sea salt (nss) sulfate, ammonium, and nitrate. During wildfire periods, nss K mass concentrations were not enhanced as strongly as other species in the sub-micrometer stages and even decreased in the super-micrometer stages; species other than nss K are more reliable tracers for biomass burning in this region. Chloride levels were reduced in the fire sets likely due to chloride depletion by inorganic and organic acids that exhibited elevated levels in transported plumes. During wildfire periods, the mass size distribution of most dicarboxylic acids changed from unimodal to bimodal with peaks in the 0.32 mm and 1.0e1.8 mm stages. Furthermore, sulfate's peak concentration shifted from the 0.32 mm to 0.56 mm stage, and nitrate also shifted to larger sizes (1.0 mm to 1.8e3.2 mm stages). Mass concentrations of numerous soil tracer species (e.g., Si, Fe) were strongly enhanced in samples influenced by wildfires, especially in the sub-micrometer range. Airborne cloud water data confirm that soil species were associated with fire plumes transported south along the coast. In the absence of biomass burning, cloud condensation nuclei (CCN) composition is dominated by nss sulfate and ammonium, and the water-soluble organic fraction is dominated by methanesulfonate, whereas for the samples influenced by wildfires, ammonium becomes the dominant overall species, and oxalate is the most abundant organic species. a r t i c l e i n f o

Elemental Mixing State of Aerosol Particles Collected in Central Amazonia during GoAmazon2014/15

“…Together with the appreciable amount of P and K, this results in the higher particle diversity seen in this cluster. Further supporting this cluster's identity is that enhancement of these elements have been observed previously during biomass burning events in the presence of a background rich in marine aerosols [64,65]. [61,62].…”

Stratocumulus Cloud Clearings and Notable Thermodynamic and Aerosol Contrasts across the Clear–Cloudy Interface

“…The cloudy side organic mass concentration at wheels-in and FT altitudes was greater than any other concentrations observed in the three flights. showed that continental air masses often influence layers above the stratocumulus cloud deck in the study region even though the bulk low-level flow is alongshore; during this flight, biomass-burning plumes were being advected and mixed into the study region from near the OregonCalifornia border (Maudlin et al 2015) that are likely linked to the enhanced organic levels observed.…”

Aerosol characteristics in the entrainment interface layer in relation to the marine boundary layer and free troposphere

“…4). With regard to emissions sources that could promote nucleation in the study region, major ones include shipping (e.g., SO 2 ; Coggon et al, 2012), marine biogenic emissions (e.g., dimethylsulfide, amines; Sorooshian et al, 2009Sorooshian et al, , 2015Youn et al, 2015), and continental emissions (e.g., NH 3 , volatile organic compounds; Maudlin et al, 2015;Braun et al, 2017). The combination of cool and moist air, high actinic solar fluxes, relatively low SA concentrations as compared to other studies with nucleation events (e.g., Alam et al, 2003;Cai et al, 2017), and several precursor vapor sources builds a case for why nucleation resulted in the highest number concentration of particles with D p between 3 and 10 nm in the EIL relative to other vertical layers.…”