Abstract
Abstract. Combustion of hydrocarbons produces both particulate- and gas-phase emissions responsible for major impacts on atmospheric chemistry and human health. Ascertaining the impact of these emissions, especially on human health, is not straightforward because of our relatively poor knowledge of how chemical compounds are partitioned between the particle and gas phases. Accordingly, we propose coupling a two-filter sampling method with a multi-technique analytical approach to fully characterize the particulate- and gas-phase compositions of combustion by-products. The two-filter sampling method is designed to retain particulate matter (elemental carbon possibly covered in a surface layer of adsorbed molecules) on a first quartz fiber filter while letting the gas phase pass through and then trap the most volatile components on a second black-carbon-covered filter. All samples thus collected are subsequently subjected to a multi-technique analytical protocol involving two-step laser mass spectrometry (L2MS), secondary ion mass spectrometry (SIMS), and micro-Raman spectroscopy. Using the combination of this two-filter sampling–multi-technique approach in conjunction with advanced statistical methods, we are able to unravel distinct surface chemical compositions of aerosols generated with different set points of a miniCAST burner. Specifically, we successfully discriminate samples by their volatile, semi-volatile, and non-volatile polycyclic aromatic hydrocarbon (PAH) contents and reveal how subtle changes in combustion parameters affect particle surface chemistry.
Highlights
Particulate matter (PM) produced by incomplete combustion of hydrocarbon-based fuels is often found associated with gas-phase compounds that include carbon and nitrogen oxides (CO, CO2, and NOx), along with a volatile fraction of organic species encompassing low-mass polycyclic aromatic hydrocarbons (PAHs)
Front and back filters generated are representative of the exhaust stream and are subsequently analyzed through first an original L2MS technique featuring three ionization schemes, followed by secondary ion mass spectrometry (SIMS), and last micro-Raman spectroscopy
We determined that PM is essentially sampled on front filters, whereas the dominant compounds trapped on all back filters were volatile PAHs regardless of the combustion conditions
Summary
Particulate matter (PM) produced by incomplete combustion of hydrocarbon-based fuels is often found associated with gas-phase compounds that include carbon and nitrogen oxides (CO, CO2, and NOx), along with a volatile fraction of organic species encompassing low-mass polycyclic aromatic hydrocarbons (PAHs). In the current European air quality legislation (European Fourth Air quality Daughter Directive 2004/107/EC), seven potentially harmful PAHs must, at least, be monitored, but restrictions on PAH concentrations are currently solely limited to benzo[a]pyrene because of its recognized high toxicity (annual target value of 1 ng m−3 in the PM10 particulate-phase fraction; Pandey et al, 2011). It is the conjunction of the PM intrinsic physicochemical properties (e.g., nature of adsorbed PAH – Dachs and Eisenreich, 2000 – or water affinity) with pressure, temperature, hygrometric variations, or aging processes in the atmosphere that condition phase partitioning (free vs bound fraction; Ravindra et al, 2006). PAHs emitted in exhausts, in either the gas phase or the particulate phase, must be analyzed and fully characterized at the same time to better understand their deposition mechanism or chemical transformation in the atmosphere and help ascertain their overall toxicity and impact on human health
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