Measuring Particulate Emissions of Light Duty Passenger Vehicles Using Integrated Particle Size Distribution (IPSD) David C. Quiros,* ,†,‡ Sherry Zhang, † Satya Sardar, † Michael a. Kamboures, † David Eiges, † Mang Zhang, † Heejung S. Jung, § Michael J. Mccarthy, † M.-C. Oliver Chang, † Alberto Ayala, † Yifang Zhu, ‡,∥ Tao Huai, †,∥ and Shaohua Hu † † California Air Resources Board 1001 I Street, Sacramento, California 95814, United States ‡ Environmental Science & Engineering, Institute of the Environment and Sustainability, La Kretz Hall, Suite 300, Los Angeles, California 90095, United States § Center for Environmental Research and Technology (CE-CERT), Bourns College of Engineering, University of California, Riverside, 1084 Columbia Avenue Riverside, California 92507, United States ∥ Department of Environmental Health Sciences, Fielding School of Public Health, University of California, Los Angeles 650 Charles E. Young Drive South, Los Angeles, California 90095, United States * S Supporting Information ABSTRACT: The California Air Resources Board (ARB) adopted the low emission vehicle (LEV) III particulate matter (PM) standards in January 2012, which require, among other limits, vehicles to meet 1 mg/mi over the federal test procedure (FTP). One possible alternative measurement approach evaluated to support the implementation of the LEV III standards is integrated particle size distribution (IPSD), which reports real-time PM mass using size distribution and effective density. The IPSD method was evaluated using TSI’s engine exhaust particle sizer (EEPS, 5.6− 560 nm) and gravimetric filter data from more than 250 tests and 34 vehicles at ARB’s Haagen-Smit Laboratory (HSL). IPSD mass was persistently lower than gravimetric mass by 56−75% over the FTP tests and by 81−84% over the supplemental FTP (US06) tests. Strong covariance between the methods suggests test-to-test variability originates from actual vehicle emission differences rather than measurement accuracy, where IPSD offered no statistical improvement over gravimetric measurement variability. 1. INTRODUCTION Chronic exposure to ambient particulate matter (PM), a mixture of natural and anthropogenic solid and semivolatile constituents, is associated with increased cardiopulmonary morbidity and mortality. 1,2 Exposure to primary PM from mobile sources has been well characterized, 3−9 and has been linked directly to adverse health outcomes. 10−12 Over the past decades, the California Air Resources Board (ARB) has implemented several mobile source control programs resulting in widespread emission reductions, 13 and ARB adopted PM standards for the low emission vehicle (LEV) III standards as part of the Advanced Clean Cars program. Beginning with model year (MY) 2017 and MY 2025, the current 10 mg/mi PM standards will decrease to 3 mg/mi and 1 mg/mi, respectively, over the Federal Test Procedure (FTP). 14 LEV III standards also include PM standards applicable to the Supplemental FTP (US06) test cycle, as well as higher interim in-use emission limits. One stated objective of the LEV III standards was to ensure future vehicles continue to have very low PM emissions. Current gasoline vehicles commonly use port-fuel injection (PFI) and typically overcomply with the current 10 mg/mi standard. However, some newer technologies being introduced to meet increasingly stringent greenhouse gas emission standards, such as gasoline direct injection (GDI), have been shown to comply by a smaller margin 15−17 and the measure- ment precision at the new standards, especially at 1 mg/mi, was not thoroughly investigated. Since the adoption of the LEV III standards, ARB has confirmed the feasibility of gravimetric measurement of PM emissions below 1 mg/mi using the existing filter-based gravimetric method. 18 PM emission standards in the United States have thus far been defined on a filter-based mass basis, which to date remains the reference method for measuring PM. Nevertheless, alternative metrics used to define, measure, and control PM emissions is critical to Received: February 5, 2015 Revised: April 15, 2015 Accepted: April 16, 2015 Article pubs.acs.org/est © XXXX American Chemical Society A DOI: 10.1021/acs.est.5b00666 Environ. Sci. Technol. XXXX, XXX, XXX−XXX