Cloud Condensation Nuclei Activity and Hygroscopicity of Fresh and Aged Biomass Burning Particles

Abstract

Biomass burning particles are one of the largest aerosol sources worldwide and contribute a significant fraction of the global cloud condensation nuclei (CCN) burden. Chemical aging experiments of sawgrass burning particles took place in a smog chamber by turning on the UV light after HONO or H 2 O 2 injection. The CCN activity and corresponding hygroscopicity of fresh and aged particles were measured. Most of the fresh particles can serve as reasonable CCN, and the average activation diameters at 0.2% supersaturation were 114-125 nm in the experiments. The aging process caused that the mass fraction of organic aerosols decrease and condensed phase nitrate NO 3 increase, and also the average atomic oxygen to carbon (O:C) ratios increase, which were the main reasons that the aged particles were more CCN active and hygroscopic. The average activation diameters decreased by 8-15% at 0.2% supersaturation after aging, and hygroscopic parameter j increased by 30-42%. The chemical aging productions were a little different in experiments, but the CCN property and hygroscopicity change trends were quite similar.

Morphology of Organic Carbon Coatings on Biomass-Burning Particles and Their Role in Reactive Gas Uptake

“…Nitrous (HONO) and nitric (HNO 3 ) acids were the likely reactants during our experiments, however the uptake of related nitrogen oxides such as the nighttime NO x reservoir N 2 O 5 may be comparably affected by organic coatings, as was theorized in prior work. , Fuel identity and combustion conditions are two factors that likely affect the nature of the organic carbon material emitted during combustion. These results provide insight into the inconsistent observations of chloride displacement in ambient and laboratory , measurements and suggest that organic material within and around atmospheric particles will affect a variety of processes, such as the uptake of reactive gases ,,, and water , and the partitioning of semivolatile organic and inorganic components under a range of atmospheric conditions.…”

“…Biomass-burning aerosol (BBA) is a significant source of atmospheric aerosol on both regional and global scales, impacting local air quality and the aerosol burden in the troposphere and stratosphere. , The prevalence and potential importance of BBA is likely to increase over the coming years as changes in climate and land-use drive increases in the frequency and extent of wildfires. − BBA affects atmospheric radiative forcing, , cloud dynamics, and microphysics by acting as cloud condensation nuclei , or ice-nucleating particles , at regional and global scales and facilitates multiphase chemical reactions . At the single-particle level, the climate-forcing and multiphase-reactivity properties of BBA and their effects on the atmosphere are determined by the composition and mixing state of each particle.…”

“…The organic material will then typically exist at the particle surface and can impede reactive processes such as uptake of N 2 O 5 (g), HNO 3 (g), or H 2 SO 4 (g) that drives particulate chloride displacement ,, to the gas phase as ClNO 2 (g) or HCl­(g). These reactions will also alter particle hygroscopicity and water uptake, phase transitions, pH, and thus aqueous chemical reactions. ,,− Chloride displacement reactions are also significant because of the differing hygroscopic behavior, phase transitions, and solubilities of chloride and the nitrate, sulfate, or organic phases that form through these gas–particle reactions. , The effects of organic carbon particle coatings on gas reactive uptake depend on particle composition, the gas-phase reactant, and ambient atmospheric conditions such as relative humidity that control phase transitions, particle phase, and water content. ,,− For example, our prior measurements of N 2 O 5 reactive uptake and ClNO 2 formation from BBA observed low and inconsistent yields and postulated this could be related to particle morphology or phase state. , Our recent experiments where the BBA was exposed to higher relative humidities above typical salt deliquescence points prior to exposure to N 2 O 5 confirmed that chloride reactivity in BBA can be impeded by organic coatings and solid and thus less reactive effloresced chloride phases …”

Biomass combustion produces ice-active minerals in biomass-burning aerosol and bottom ash

“…Biomass burning represents an important component of the global aerosol burden (11)(12)(13)(14)(15) and can be a major episodic and regional source of particulate matter (11,13,14,16,17). Biomass-burning aerosol (BBA) has been observed to undergo long-range transport (13,15,18) and to affect cloud properties by acting as cloud condensation nuclei (18)(19)(20) and INPs (18,21,22) over large regional extents. Changes in land use and climate at global and regional scales are predicted to increase the frequency, intensity, and scale of wildfires and prescribed burns over the coming years (23)(24)(25)(26)(27), making BBA an even more important perturbation to Earth's atmosphere and climate systems in the near future.…”

Three-Dimensional Distribution of Biomass Burning Aerosols from Australian Wildfires Observed by TROPOMI Satellite Observations

“…They can produce a warming or cooling radiative forcing, depending on their optical properties and then their atmospheric lifetime [3]. If vertically and horizontally co-located with clouds, they may modify their properties and precipitation by acting as cloud condensation nuclei, e.g., [4], depending on the age and the composition of the particles, e.g., [5]. When transported near the surface, BB aerosols degrade air quality and cause negative long-term health effects, e.g., [6].…”