High Viscosity and Two Phases Observed over a Range of Relative Humidities in Biomass Burning Organic Aerosol from Canadian Wildfires.

Biomass burning organic aerosol (BBOA) is a major contributor to organic aerosol in the atmosphere. The impacts of BBOA on climate and health depend strongly upon their physicochemical properties, including viscosity and phase behavior (number and types of phases); these properties are not yet fully characterized. We collected BBOA field samples during the 2021 British Columbia wildfire season to constrain the viscosity and phase behavior at a range of relative humidities and compared them to previous studies on BBOA.

Secondary Organic Aerosol from Biomass Burning Phenolic Compounds and Nitrate Radicals can be Highly Viscous over a Wide Relative Humidity Range.

Biomass burning events, including wildfires, can emit large amounts of phenolic compounds such as guaiacol. These phenolic compounds can undergo oxidation by nitrate radicals (NO) to form secondary organic aerosol (SOA). Viscosity and hygroscopicity are key properties that affect SOA's role in atmospheric chemistry, air quality, climate and public health.

Phase Behavior of Internal Mixtures of Hydrocarbon-like Primary Organic Aerosol and Secondary Aerosol Based on Their Differences in Oxygen-to-Carbon Ratios.

The phase behavior, the number and type of phases, in atmospheric particles containing mixtures of hydrocarbon-like organic aerosol (HOA) and secondary organic aerosol (SOA) is important for predicting their impacts on air pollution, human health, and climate. Using a solvatochromic dye and fluorescence microscopy, we determined the phase behavior of 11 HOA proxies (O/C = 0-0.29) each mixed with 7 different SOA materials generated in environmental chambers (O/C 0.

Characterizing non-photochemical quenching in leaves through fluorescence lifetime snapshots.

We describe a technique to measure the fluorescence decay profiles of intact leaves during adaptation to high light and subsequent relaxation to dark conditions. We show how to ensure that photosystem II reaction centers are closed and compare data for wild type Arabidopsis thaliana with conventional pulse-amplitude modulated (PAM) fluorescence measurements. Unlike PAM measurements, the lifetime measurements are not sensitive to photobleaching or chloroplast shielding, and the form of the fluorescence decay provides additional information to test quantitative models of excitation dynamics in intact leaves.