UC Berkeley

Organic carbon in the atmosphere fuels the formation of ozone and comprises a large fraction of fine particulate matter, both of which are detrimental to human health. Particulate matter additionally is a source of uncertainty in radiative forcing predictions, hindering predictions of climate change impacts. Atmospheric organic carbon is complex, consisting of thousands of different compounds and covering more than 15 orders of magnitude in volatility (vapor pressure) and widely varying chemical reactivity. Many of these compounds serve as specific indicators of pollution sources or atmospheric chemical processes. In this work, two different advanced custom instruments for measurement of speciated volatile, intermediate volatility and semivolatile organic compounds (VOCs, IVOCs and SVOCs) are used to elucidate and profile the sources of pollution in distinct atmospheric environments. One of these instruments is introduced for the first time along with its design and development details.

Chapter 2 presents a suite of semivolatile markers of fresh biomass burning (BB) measured at a rural site in Amazonia, Brazil by the Semivolatile Thermal desorption Aerosol Gas chromatograph (SV-TAG), which specializes in hourly speciated measurements of IVOCs and SVOCs and their partitioning between the gas and particle phases. These 16 markers are found to comprise the majority of fresh BB organic aerosol. Despite much greater concentrations in the dry season versus the wet season, the BB markers comprise about the same fraction of total organic aerosol in both the dry and wet seasons. Composition of individual BB events and atmospherically aged air parcels were highly variable but provide a chemical profile of fresh BB in the Amazon.

By combining traditional speciated VOC measurement instrumentation with the SV-TAG, the Comprehensive Thermal desorption Aerosol Gas chromatograph (cTAG) is sensitive to a wider range of volatility of reactive organic carbon. cTAG joins a layered bed of adsorbents for VOC and IVOC collection and a reusable metal mesh filter for SVOC collection together before a single mass spectrometer, providing consistent quantification across the volatility range. Chapter 3 presents design and development details for cTAG, including VOC and IVOC collector design optimization, performance of a custom liquid evaporation system for VOCs and IVOCs, and verification that ozone removal is effective while not perturbing measured concentrations of nonreactive compounds. Potential applications of this instrument are presented using a brief analysis of field data.

Chapter 4 analyzes major sources of pollution in suburban Livermore, California using measurements of 123 VOCs, IVOCs and SVOCs collected by cTAG. Positive Matrix Factorization on the generated timelines yields 13 distinct factors representing different sources and processes in the atmosphere, including gasoline exhaust, consumer products, biomass burning, secondary oxidation, emissions from evaporative sources and more. Monoterpenoid mass was present in greater quantities in the consumer product factor than biogenic sources, consistent with recent observations in other urban contexts. Several factors contained significant mass from measurements on both channels of cTAG, indicating that the expanded volatility range afforded by cTAG led to more complete chemical characterization of those sources.

The final chapter notes directions for future research and explores measurement and analysis opportunities for cTAG.