title: First online measurements of sulfuric acid gas in modern heavy-duty diesel engine exhaust: implications for nanoparticle formation.
abstract: To mitigate the diesel particle pollution problem, diesel vehicles are fitted with modern exhaust after-treatment systems (ATS), which efficiently remove engine-generated primary particles (soot and ash) and gaseous hydrocarbons. Unfortunately, ATS can promote  formation of low-vapor-pressure gases, which may undergo nucleation and condensation leading to  formation of nucleation particles (NUP). The chemical nature and formation mechanism of these particles are only poorly explored. Using a novel mass spectrometric method,  online measurements of low-vapor-pressure gases were performed for  exhaust of a modern heavy-duty diesel engine operated with modern ATS and combusting low and ultralow sulfur fuels and also biofuel. It was observed that the gaseous sulfuric acid (GSA) concentration varied strongly, although  engine operation was stable. However, the exhaust GSA was observed to be affected by fuel sulfur level, exhaust after-treatment, and driving conditions. Significant GSA concentrations were measured also when biofuel was used, indicating that GSA can be originated also from lubricant oil sulfur. Furthermore, accompanying NUP measurements and NUP model simulations were performed. We found that the exhaust GSA promotes NUP formation, but also organic (acidic) precursor gases can have a role. The model results indicate that that the measured GSA concentration alone is not high enough to grow the particles to the detected sizes.
authors.affiliation: Max Planck Institute for Nuclear Physics (MPIK), P.O. Box 103980, D-69029 Heidelberg, Germany. frank.arnold@mpi-hd.mpg.de
authors.forename: F
authors.initials: F
authors.lastname: Arnold
authors.forename: L
authors.initials: L
authors.lastname: Pirjola
authors.forename: T
authors.initials: T
authors.lastname: Rönkkö
authors.forename: U
authors.initials: U
authors.lastname: Reichl
authors.forename: H
authors.initials: H
authors.lastname: Schlager
authors.forename: T
authors.initials: T
authors.lastname: Lähde
authors.forename: J
authors.initials: J
authors.lastname: Heikkilä
authors.forename: J
authors.initials: J
authors.lastname: Keskinen
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods*; D013058:Mass Spectrometry / Q000379:methods*; D053758:Nanoparticles / Q000032:analysis*; D010316:Particle Size; D013464:Sulfuric Acids / Q000032:analysis*; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D013464:Sulfuric Acids; D001335:Vehicle Emissions; C033158:sulfuric acid