AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Real-time Sampling of Total Biogenic Volatile Organic Compounds Using a Compact, Portable Photoionization Detector
MATTHEW STEWART, Jianhuai Ye, Tianning Zhao, Karena McKinney, Scot T. Martin, Harvard University
Abstract Number: 282 Working Group: Air Quality Sensors: Low-cost != Low Complexity
Abstract The biosphere emits a complex mixture of volatile organic compounds (VOCs) of varying reactivities into the atmosphere. Many of these are highly reactive components that can significantly influence the overall chemical reactivity of the atmosphere even at very low (sub-ppbv) concentrations. VOC concentrations also vary markedly over small spatial (10’s to 100’s of meters) and time (seconds to minutes) scales. In order to fully quantify VOC emissions and chemistry, measurements that capture this spatial and temporal variability are needed. Traditional techniques for measuring VOCs have been limited by several factors, including high cost, low portability, and, in some cases, slow response time, constraining their ability to fully capture the spatial variation in VOC concentrations in particular. In addition, while measurements of speciated VOCs are valuable for understanding the relationship between ecosystem types and emissions or detailed chemical mechanisms, measures of total VOCs and their reactivity would be valuable in helping to close the gap between the sum of observed individual concentrations and total reactivity that has been observed in some studies.
In this work, we present a method for estimating ambient outdoor concentrations of total biogenic VOCs, a proxy for the collective behavior of VOCs and their net effects on oxidation capacity, in real time using a photoionization detector (PID). PIDs are a mature sensor technology commonly used as detectors within gas chromatograms and for indoor air quality monitoring, but several challenges, such as sensitivity to temperature, humidity, chemical species, and its inherent non-selectivity, have hindered their implementation for ambient outdoor sampling of VOCs. Through a combination of laboratory and chamber studies, robust calibration procedures using isoprene, α-pinene, and β-caryophyllene were developed for estimating total biogenic VOCs using high-sensitivity commercial PIDs. These procedures manage the humidity and temperature sensitivities typically associated with PIDs to provide accurate and repeatable measurements when compared to a proton transfer reaction mass spectrometer.
Field tests to validate the accuracy of measured total VOC concentrations are planned in temperate and tropical forests, with the eventual aim of performing real-time aerial measurements using civilian unmanned aerial vehicles. PIDs offer a portable means to obtain measurements of total biogenic VOCs with high time resolution, which provide atmospheric scientists with new ways to help to constrain VOC emission estimates, as well as to attribute unexplained reactivity to highly reactive organic species.