Chemical composition of PM<sub>2.5</sub> in October 2017 Northern California wildfire plumes

Abstract

Abstract. Wildfires have become more common and intense in the western US over recent decades due to a combination of historical land management practices and warming climate. Emissions from large-scale fires now frequently affect populated regions such as the San Francisco Bay Area during the fall wildfire season, with documented impacts of the resulting particulate matter on human health. Health impacts of exposure to wildfire emissions depend on the chemical composition of particulate matter, but the molecular composition of the real biomass burning organic aerosol (BBOA) that reaches large population centers remains insufficiently characterized. We took PM2.5 (particles having aerodynamic diameters less than or equal to 2.5 µm) samples at the University of California, Berkeley campus (∼ 60 km downwind of the fires) during the October 2017 Northern California wildfires period and analyzed molecular composition of OA using a two-dimensional gas chromatography coupled with high-resolution time-of-flight mass spectrometry (GC×GC HR-ToF-MS). Sugar-like compounds were the most abundant component of BBOA, followed by mono-carboxylic acids, aromatic compounds, other oxygenated compounds, and terpenoids. The vast majority of compounds detected in smoke have unknown health impacts. Regression models were trained to predict the saturation vapor pressure and averaged carbon oxidation state (OSc‾) of detected compounds. The compounds speciated have a wide volatility distribution and most of them are highly oxygenated. In addition, time series of primary BBOA tracers observed in Berkeley were found to be indicative of the types of plants in the ecosystems burned in Napa and Sonoma, and could be used to differentiate the regions from which the smoke must have originated. Commonly used secondary BBOA markers like 4-nitrocatechol were enhanced when plumes aged, but their very fast formation caused them to have similar temporal variation as primary BBOA tracers. Using hierarchical clustering analysis, we classified compounds into seven factors indicative of their sources and transformation processes, identifying a unique daytime secondary BBOA factor. Chemicals associated with this factor include multifunctional acids and oxygenated aromatic compounds. These compounds have high OSc‾, and they are also semi-volatile. We observed no net particle-phase organic carbon formation, which indicates an approximate balance between the mass of evaporated organic carbonaceous compounds and the addition of secondary organic carbonaceous compounds.

Soot PCF: pore condensation and freezing framework for soot aggregates

“…Soot forms aggregates that are composed of primary carbon spheres, characterized by an onion-shell structure of folded graphite sheets, which typically have diameters D pp of between 10 and 45 nm but that can also reach larger values (e.g. Kim et al, 2001;Liati et al, 2014;Megaridis and Dobbins, 1990;Wentzel et al, 2003). The primary particles coagulate to form soot clusters that grow further in size into soot aggregates as a result of monomer-cluster or clustercluster collision.…”

“…Burtscher, 2005;Ferraro et al, 2016;Smekens et al, 2005;Su et al, 2004), aircraft turbines (e.g. Delhaye et al, 2017;Liati et al, 2014Liati et al, , 2019Marhaba et al, 2019;Smekens et al, 2005), and commercial carbon blacks and/or soot generated from controlled flames in the laboratory (e.g. Clague et al, 1999;Cortés et al, 2018;Ferraro et al, 2016;Megaridis and Dobbins, 1990;Ouf et al, 2016Ouf et al, , 2019.…”

“…Clague et al, 1999;Cortés et al, 2018;Ferraro et al, 2016;Megaridis and Dobbins, 1990;Ouf et al, 2016Ouf et al, , 2019. For instance, Liati et al (2014) used TEM images to investigate the size of primary particles of a turbofan engine (type CFM56-7B26/3), frequently used in Boeing 737 aircraft, that was operated with standard Jet A-1 fuel. They reported the primary particle diameter to increase with increasing thrust level.…”

Grazing in California's Mediterranean Multi-Firescapes

“…Overall, the state faces deadly wildfires of increasing size, frequency, and intensity, and growing in costs (Figure 2). The collateral damage is serious and affects all Californians: smoke threatens human health in the cities as well as near the wildlands (Koman et al, 2019;Liang et al, 2021); carbon emissions and loss of carbon stock contribute to climate change (North and Hurteau, 2011), and costs add to the public ledger (Diaz, 2012;Kousky et al, 2018). For those directly affected by fires, lives and homes are lost, businesses are destroyed, the landscape of home is profoundly changed (Waks et al, 2019).…”

Diffusion Coefficients and Mixing Times of Organic Molecules in β-Caryophyllene Secondary Organic Aerosol (SOA) and Biomass Burning Organic Aerosol (BBOA)

“…Biomass burning organic aerosol (BBOA) is another abundant type of aerosol in the atmosphere. ,− In contrast to SOA, BBOA is emitted directly to the atmosphere during the combustion of vegetation, including forests and crop residues. ,− The chemical composition and properties of BBOA will depend on both the fuel type and the combustion conditions. − Like SOA, BBOA also consists of many different organic molecules. BBOA also includes light-absorbing organic molecules, referred to as brown carbon, that can have a large positive radiative effect on the Earth–Atmosphere system. − …”