Metallic and Crustal Elements in Biomass-Burning Aerosol and Ash: Prevalence, Significance, and Similarity to Soil Particles

Abstract

The morphology and composition of laboratory-generated biomass-burning aerosol (BBA) and bottom ash particles from authentic fuels were determined using transmission and scanning electron microscopies (TEM/SEM) and single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-ToF-MS). BBA particles with mineral material identified through elemental analysis using SEM represented 3−25% of the individual BBA particle numbers analyzed. This percentage varied depending on the fuel, with BBA from grass fuels containing more mineral particles than BBA from ponderosa pine wood. TEM analysis showed that these particles typically consist of carbonaceous material and a small (50−500 nm) region rich in nonvolatile elements. We also performed SEM/EDX analysis on soil, mineral BBA, and ash particles to measure Si:Al:Fe ratios and show that each of these particle classes possesses a different average bulk composition. However, individual particles within each population possess varying Si:Al:Fe ratios that may not be sufficiently unique to consistently determine particle sources from single-particle analysis. Mineral regions in BBA particles were similar in composition to residual bottom ash particles but were more likely to contain mixtures of nonvolatile elements, suggesting that ash particles typically underwent more complete combustion and mineralization. Multielement sp-ICP-ToF-MS analysis confirmed the presence of mineral particles in BBA, ash, and soil samples, with the most prevalent elements being the common crustal elements Al, Si, and Fe. Zn-and Ti-bearing particles were identified in both ash and soil samples, with more Zn present in ash particles and more Ti present in soil particles, suggesting that both of these types of particles would be prevalent in ambient measurements of BBA and biomass-burning impacted air masses. The mineral phases present in combustion-derived mineral phases are likely distinct from those present in soil-derived particles and may significantly affect the bulk properties of biomass-burning smoke. Both mineral BBA particles and lofted ash are likely sources of bioavailable iron and phosphorus that have been measured in biomass-burning emissions. These combustion-generated mineral phases are also important sources of ice-nucleating particles that have recently been reported in biomass-burning aerosol and bottom ash.

Cloud Activation via Formation of Water and Ice on Various Types of Porous Aerosol Particles

“…Finally, we consider the behavior of pores occurring in aggregates of primary spherules and calculate the corresponding ice and liquid water pore filling and escape conditions. Aggregate particles are abundant in the atmosphere ,− and for some of them ice nucleating abilities have been reported. , Figure a depicts an exemplary aggregate (top) as well as an enlarged profile view of a section of it. We simplified this rather complicated type of pore geometry by assuming a rotational symmetry, see Section 5 of the Supporting Information and Figure S6 for more details.…”

“…Our calculations indicate that particular aggregate clusters of primary particles may be important CCN or INP in the atmosphere. Such aggregates have been observed to occur readily in the atmosphere, for example, in the form of soot, fly ash, biological particles, and biomass-burning-derived mineral aerosol and bottom ash particles. ,,− Clearly, this atmospheric variety as well as the complex structure of such agglomerates may require dedicated consideration for calculating the corresponding saturation curves. In the Supporting Information, we provide a detailed scheme that employs representative geometrical parameters and that is suited for describing a wide range of such aggregate geometries and their corresponding pore filling processes, respectively.…”

Response of the Reaction Probability of N2O5 with Authentic Biomass-Burning Aerosol to High Relative Humidity

“…Yet, the reactive uptake coefficient of N 2 O 5 (γ­(N 2 O 5 )) and nitryl chloride yield (φ­(ClNO 2 )) have important atmospheric implications and are known to depend on particle composition, water content, and morphology. High water content increases γ­(N 2 O 5 ) by promoting hydrolysis, and the resulting particulate nitrate can reduce γ­(N 2 O 5 ) by up to an order of magnitude in what is called the “nitrate effect” (). , Particulate chloride can enhance γ­(N 2 O 5 ) and lead to ClNO 2 formation. ,, Organic carbon coatings have also been shown to reduce γ­(N 2 O 5 ), and primary organic aerosol makes up a large mass fraction of BBA and may be present as coatings. ,− The organic carbon component of BBA is a complex mixture of primary and secondary molecules that can undergo heterogeneous and particle-phase reactions, precluding generalizable estimates of organic aerosol composition or properties. , Until recently, γ­(N 2 O 5 ) has only been determined with simplified one- or two-component aerosol systems or BBA proxies ,,,, that may not represent authentic BBA and its complex composition and morphology. ,− …”

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

“…Most BBA compositional studies have focused on the carbonaceous and inorganic salt components, which comprise the majority of the aerosol mass in biomass-burning emissions. , Here, we use inorganic salt particles to refer to the most common inorganic phases found in fresh or aged BBA, composed of soluble salts of the cations K + , Na + , or NH 4 + and the anions Cl – , NO 3 – , or SO 4 2– , in contrast to mineral inorganic phases composed of metallic or crustal elements. , However, gaps remain in our understanding of how particle composition, mixing state, and surface characteristics combine to determine the key properties and reactivity of a particle. The particle surface is significant in this regard as it mediates interactions between the particle and reactive and condensable vapors, sunlight, and water vapor.…”