AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Prediction of Organic Aerosol Precursor Emission from Wood Pyrolysis
MARIAM FAWAZ, Tami Bond, University of Illinois at Urbana Champaign
Abstract Number: 299 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract Emission of organic aerosols (OA) from wood combustion is responsible for a large percentage of primary organic aerosols in the atmosphere, most of which are released during the pre-ignition phase when pyrolysis is occurring. In this work, we present a pyrolysis model that predicts the release of the class of gases that includes OA precursors, called heavy gases. Temperature and mass loss in modeled pyrolysis are validated against experimental data from a controlled isothermal cylindrical reactor that gives highly reproducible pyrolysis, with instantaneous mass loss rates within 10% between replicate experiments.
We demonstrate the potential of using pyrolysis modeling in understanding the emission of OA from wood combustion. Heavy gases are the products of tar secondary reactions, where tar is formed as a condensed phase from primary pyrolysis reactions. We use the model to calculate the yield of emission and release rate of heavy gases. Maple wood of dimensions 14x3.8x2.9 cm was used at three reactor temperatures (400C, 500C, and 600C). The yield of heavy gases increased from 70% to 80% by mass when the pyrolysis temperature changed from 400C to 600C. The rate of emission of heavy gases showed one broad peak at 400C and two sharp peaks at 600C throughout pyrolysis. The magnitude of peak emission rate was higher at 600C than 400C. We attribute the multiple peaks in emission rate to the large thermal gradient that forms initially between the surface and center at high temperature. During pre-ignition, higher heat flux promotes the rapid release of heavy gases and the subsequent release of high OA during this important initial period of wood heating that precedes combustion.