AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Scooter Emissions Dominate Urban Organic Aerosol
Imad El Haddad, Stephen Platt, Alessandro Zardini, Jay Slowik, Michael Clairotte, Covadonga Astorga, Peter Barmet, Josef Dommen, Urs Baltensperger, ANDRE PRÉVÔT, Paul Scherrer Institute
Abstract Number: 91 Working Group: Urban Aerosols
Abstract In urban areas, where the health impact of pollutants increases due to higher population density, traffic is a major source of ambient organic aerosol (OA). A significant fraction of OA from traffic is secondary, produced via the reaction of exhaust precursor gases with atmospheric oxidants. Secondary OA (SOA) has not been systematically assessed for different vehicles and driving conditions and thus its relative importance compared to directly emitted, primary OA (POA) is unknown. 2-stroke (2S) scooters are inexpensive and convenient and as such are a popular means of transportation. However, as the European regulations for scooters are less stringent than for other vehicles, current estimates suggest that 2S scooters may emit more POA and SOA precursors than all other vehicles combined.
Here, we assess POA emission factors (EFs) and potential SOA production from 2S scooters. 2S scooters were run in idle or simulated low power conditions and on a chassis dynamometer, during regulatory ECE47 driving cycles. Emissions was introduced into smog chambers, where primary emissions and SOA formation were monitored using a suite of instruments including a high-resolution time-of-flight aerosol mass spectrometer and a proton transfer time-of-flight mass spectrometer.
We show that the oxidation of VOCs in the exhaust emissions of 2S scooters produce significant SOA, exceeding by up to an order of magnitude POA emissions. We show that SOA formation from 2S scooter emissions essentially stems from the condensation of aromatic oxidation products. Further, we demonstrate that replacing the standard gasoline with an aromatic-free fuel mitigates SOA production, underlining the major role of aromatic compounds from 2S exhaust on SOA production. POA and potential SOA EFs determined here from 2S scooters will be presented and compared with EFs from other vehicles (4S scooters, gasoline cars and diesel cars) to assess the contributions of 2S scooters in urban atmospheres.