10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Assessment of a Field Portable Oxidation Flow Reactor (OFR) Measurement System for Biofuel Emission Characterization in Remote and Rural Settings
ADITYA SINHA, Andrew Grieshop, North Carolina State University
Abstract Number: 1402 Working Group: Oxidation Flow Reactor: Development, Characterization, and Application to Aerosols
Abstract Oxidation flow reactor (OFR) experiments in our lab have explored the properties of secondary organic aerosol (SOA) formed from photochemical aging of emissions from cookstoves like those used by billions daily. Lab experiments have explored the physical and chemical properties of SOA formed from emissions for stove types of varying efficiencies, different fuel types (hard and soft wood) and various operating OFR conditions. The OFR simulated up to 18 days of equivalent atmospheric aging and we observed peak organic aerosol (OA) enhancements of about a factor of 3 over primary OA, dependent on stove and fuel types. However, field emission monitoring efforts have consistently shown a clear distinction between in-field performance of cookstoves and that from standardized lab tests. For instance, the primary particulate matter emission factors (PM EFs) measured in the field are often 2 or more times that in the lab1. The work presented here builds on previous experiments to develop simplified methods to quantify SOA formation potential from emissions during in-home use of biomass stoves. Typical lab experiments have characterized cookstove emissions utilizing sophisticated instrumentation like the Aerosol Chemical Speciation Monitor (ACSM) and Photoacoustic Extinctiometer (PAX). Since the ability to move and power advanced instruments is limited in remote and rural locations, we are developing an ensemble consisting of portable low power instruments to measure components of interest. We will evaluate this field-portable sensor suite – consisting of optical PM sensors measuring scattering/absorption, CO and CO2 sensors, and filters alongside corresponding lab based instrumentation to assess performance for international rural applications.
Preliminary evaluation indicates that OA enhancement, quantified in the lab using an ACSM correlates fairly well with the enhancement in light scattering coefficient (Bscat), quantified using a PAX. We observe a linear relationship between the OA enhancement and Bscat Enhancement across a range of stove efficiencies, fuel types and aging conditions. This indicates a potential to measure OA enhancement in real time with a portable sensor capable of measuring light scattering. We expect a high degree of inter-test variability in field measurements (for example, organic carbon emissions factors, OC EFs vary by a factor of 2-41) and so it is useful to have a measurement metric that can capture a range of enhancements (up to a factor of 2.8 based on lab testing) across aging equivalent to atmospheric exposure of 1 to 18 days. Filters are a standard method for determining PM, OC and elemental carbon (EC) EFs from a combustion event. In prior lab cookstove emission OFR experiments, we evaluated closure between PM from filters and parallel ACSM measurements. In these comparisons, filters under-predict the OA EFs relative to the ACSM, and so further work is required to evaluate the use of filters for measuring aged OA from an OFR. A hypothesis to be tested is that residual ozone from the OFR, (not fully denuded prior to reaching filters) interacts with and degrades filter-bound organic matter. Experiments will be designed to probe this disparity since filters are often a relatively inexpensive and operationally efficient way to gather important descriptors of OA from a combustion event. Subsequent steps will involve deployment of the OFR along with the measurement suite during the summer of 2018 in Mexico in a rural and remote setting.
References: [1] Grieshop, A. P., G. Jain, K. Sethuraman, and J. D. Marshall (2017), Emission factors of health- and climate-relevant pollutants measured in home during a carbon-finance-approved cookstove intervention in rural India, GeoHealth, 1, 222–236, doi:10.1002/2017GH000066.