Publications

Clean air policies can have significant impacts on climate in remote regions. Previous modeling studies have shown that the temperature response to European sulfate aerosol reductions is largest in the Arctic. Here we investigate the atmospheric and ocean roles in driving this enhanced Arctic warming using a set of fully coupled and slab-ocean simulations (specified ocean heat convergence fluxes) with the Norwegian Earth system model (NorESM), under scenarios with high and low European aerosol emissions relative to year 2000. We show that atmospheric processes drive most of the Arctic response. The ocean pathway plays a secondary role inducing small temperature changes mostly in the opposite direction of the atmospheric response. Important modulators of the temperature response patterns are changes in sea ice extent and subsequent turbulent heat flux exchange, suggesting that a proper representation of Arctic sea ice and turbulent changes is key to predicting the Arctic response to midlatitude aerosol forcing. Plain Language Summary Aerosols are liquid or solid particles suspended in air, which may have adverse air quality and health impacts. Sulfate aerosols also have a cooling influence on climate and can mask some of the greenhouse gas-induced global warming. While aerosol emissions are variable in space and time, their impacts are not limited to where they are emitted. In fact, studies using global climate models have shown that changing sulfur dioxide emissions in Europe can have significant impacts on Arctic climate. Here we investigate the roles of changes in atmospheric and ocean heat transport in driving these changes in the Arctic by conducting a series of climate model simulations with specified anthropogenic sulfur dioxide emissions and different ocean heat transport fluxes. We find that changes through the atmosphere play a primary role in affecting the Arctic climate. These changes are modulated by changes in sea ice extent and the energy exchange between ocean and atmosphere in the sub-Arctic. Aerosol-driven changes in ocean heat transport play a smaller, secondary role in the Arctic and tend to reduce the impacts. Our results show that the proper representation of Arctic sea ice is crucial for accurately modeling the Arctic response to changes in midlatitude aerosol forcing.

The complex array of sources and transformations of organic carbonaceous material that comprises an important fraction of atmospheric fine particle mass, known as organic aerosol, has presented a long running challenge for accurate predictions of its abundance, distribution, and sensitivity to anthropogenic activities. Uncertainties about changes in atmospheric aerosol particle sources and abundance over time translate to uncertainties in their impact on Earth's climate and their response to changes in air quality policy. One limitation in our understanding of organic aerosol has been a lack of comprehensive measurements of its molecular composition and volatility, which can elucidate sources and processes affecting its abundance. Herein we describe advances in the development and application of the Filter Inlet for Gases and Aerosols (FIGAERO) coupled to field-deployable High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometers (HRToF-CIMS). The FIGAERO HRToFCIMS combination broadly probes gas and particulate OA molecular composition by using programmed thermal desorption of particles collected on a Teflon filter with subsequent detection and speciation of desorbed vapors using inherently quantitative selected-ion chemical ionization. The thermal desorption provides a means to obtain quantitative insights into the volatility of particle components and thus the physicochemical nature of the organic material that will govern its evolution in the atmosphere. In this Account, we discuss the design and operation of the FIGAERO, when coupled to the HRToF-CIMS, for quantitative characterization of the molecular-level composition and effective volatility of organic aerosol in the laboratory and field. We provide example insights gleaned from its deployment, which improve our understanding of organic aerosol sources and evolution. Specifically, we connect thermal desorption profiles to the effective equilibrium saturation vapor concentration and enthalpy of vaporization of detected components. We also show how application of the FIGAERO HRToF-CIMS to environmental simulation chamber experiments and the field provide new insights and constraints on the chemical mechanisms governing secondary organic aerosol formation and dynamic evolution. We discuss the associated challenges of thermal decomposition during desorption and calibration of both the volatility axis and signal. We also illustrate how the FIGAERO HRToF-CIMS can provide additional insights into organic aerosol through isothermal evaporation experiments as well as for detection of ultrafine particulate composition. We conclude with a description of future opportunities and needs for its ability to further organic aerosol science.