Atmospheric volatile organic compounds (VOCs) are precursors of tropospheric ozone, carbon monoxide (CO), formaldehyde, and organic aerosol, and play a central role in hydrogen oxides (HOx) and nitrogen oxides (NOy) cycling. Terrestrial ecosystems are the dominant source of VOCs to the global atmosphere. This research will advance scientific understanding of biogenic VOC (BVOC) emissions and their atmospheric effects by addressing the following core questions: What is the landscape to regional-scale distribution of BVOC fluxes, and how do they respond to environmental forcing and phenology? What is the seasonal impact of BVOCs on CO and other key atmospheric species? What roles do BVOCs play during spring and fall in driving a chemical transition between NOx and VOC-limited regimes for ozone production? The research applies a new measurement-model approach linking tall tower BVOC measurements with Lagrangian and inverse modeling. Work will focus on isoprene, methanol, and acetone - three of the most ubiquitous and important BVOCs. Specific tasks will include: 1) Measure BVOC and CO concentrations at an Ameriflux tall tower (244 m) in the US Midwest. Measurements will span two full annual cycles. 2) Analyze the VOC concentrations and variability in relation to upstream sources, landcover, and season. This unique dataset will yield new insights into the controls on atmospheric VOC abundance and chemical impacts on timescales from minutes to years. 3) Relate the measurements quantitatively to regional sources using the Stochastic Time- Inverted Lagrangian Transport (STILT) model and state-of-science emission inventories. 4) Apply a formal Bayesian inverse analysis to place new constraints on landscape-to-regional scale (~ 100 - 1,000 km) BVOC sources. 5) Explore the seasonal dependence of emissions and the resulting photochemical effects on CO and other key species.
Broader impact and outreach components of the work include: 1) Broadening the participation of underrepresented students in Earth Science research through a partnership with the McNair Scholars program; 2) Training graduate students in cutting-edge atmospheric chemistry measurement and modeling tools; 3) Developing a new model-measurement tool that should be broadly useful to the scientific community; 4) Active dissemination of scientific findings through conference presentations and scientific publications. Finalized data will be made public and readily available online.
For this project we made continuous measurements of reactive carbon compounds in the atmosphere (volatile organic compounds, VOCs, and carbon monoxide, CO) at a tall tower (244 m height) observatory in the US Upper Midwest. Measurements were continued over a period of 3 years. Measurements are made at a sampling height of 185m above ground level, providing a high-resolution signal with regional-scale footprint. The tower is located in Minnesota, near the intersection of the major North American ecosystems (eastern deciduous forest, northern coniferous forest, agriculture, and western prairie), and is at times downwind of the Twin Cities metropolitan area, thus affording information on emissions from some of the most important US landscapes as well as from anthropogenic sources. We employed the data in combination with atmospheric models to test and improve current scientific knowledge of the emission sources and atmospheric impacts of key reactive carbon compounds. This work has led to: - a better understanding of the importance of natural emissions from vegetation as a source of atmospheric methanol and acetone, the two most abundant non-methane organic gases in the atmosphere - new information on how such emissions vary seasonally, and their magnitude relative to human-caused emissions - new constraints on the accuracy of current emission estimates for air pollutants such as CO, benzene, toluene, and xylenes - improved knowledge of the chemical impacts of these reactive carbon compounds on atmospheric composition. Results of this project have been published in the scientific peer-reviewed literature, and provide needed information that will help in developing improved models for predicting atmospheric composition and air quality. This project also contributed to the education and training of 1 PhD student, 1 postdoctoral researcher, and 2 undergraduate students in atmospheric chemistry and associated measurement and modeling techniques.
