Grantee Research Project Results

The objective of the proposed work is to improve emission inventories of gas-phase low volatility organic compounds (LVOCs) from mobile sources, providing inputs to microphysical/ chemical modules important for air quality predictions. Present inventories of LVOCs are limited to total mass, or concentrations of only a few species, with little information about the chemistry or volatility of the total emissions.

The focus of Year 3 activities for this project was the detailed analysis of measurements made of the emissions from a chocked DC-8 aircraft, as part the Alternative Aviation Fuels Experiment (AAFEX-2, April 2011, Palmdale CA). measurements taken over an entire “power sweep” (from 4% power up to 80%) show that LVOC emissions are highest during engine-idle operating conditions, with decreasing but non-zero LVOC emissions at higher engine powers. Comparison of LVOC emissions with total hydrocarbon (THC) measurements, VOC measurements, and an established emissions profile indicates that LVOCs comprise 10-20% of the total organic gas phase emissions at idle, and an increasing fraction of the total gas-phase organic emissions at higher powers. Positive matrix factorization (PMF) of online mass spectra is used to identify three distinct types of LVOC emissions: aliphatic hydrocarbon, aromatic hydrocarbons and oxygenated organic species. The volatility profile and power dependences allow for a relatively complete picture of the sources of these various organic classes: the volatility and chemical composition of the emissions suggest that unburned fuel is the dominant source of LVOCs at idle, while pyrolysis products make up an increasing fraction of the LVOCs at higher powers. Oxygenated LVOC emissions were detected at lower engine powers (≤ 30%) and may be linked to cracked, partially oxidized or unburned fuel components. This work demonstrates the utility of measuring LVOC emissions using online mass spectrometry; this approach is currently being applied towards the analysis of a related dataset, the measurements of emissions from a medium duty diesel engine under a range of engine loads, engine speeds, fuel types, and emissions control technology.

The focus of Year 4 of this project (as part of an approved no-cost extension) is the analysis, interpretation, and publication of our engine lab measurements (made in November 2011). The analysis approaches and scripts developed for the AAFEX data are being applied towards our measurements of LVOC emissions from the medium-duty diesel engine emissions, in order to understand LVOC loading, volatility, elemental composition (from high-resolution mass spectrometric data), and broad chemical characteristics (from positive matrix factorization) as a function of engine speed/load, fuel type, and aftertreatment. The particular focus of our analysis is on transient emissions, such as cold starts, power changes, and DPF regenerations.