1. Top Down Emission Analyses Theme 17 th GEIA Conference Nov. 19, 2015 Alex Guenther Department of Earth System Science University of California, Irvine CA USA Aircraft eddy covariance direct flux measurements - Some advances and issues - Recent results: Airborne observations of tropical forest isoprene emissions

2. Tower Temporal variations Short-term: Hours to days Long-term: Months to years Spatial variations Small-scale:Large-scale Aircraft Satellite Platforms Advance #1: Observations across scales 2 km global 30 km

3. 3 Isoprene is often the dominant sink for OH. OH is often the dominant sink for isoprene. We previously used this relationship to estimate isoprene emissions based on an assumed OH conc. (e.g., Ayers and Gillett 1988, Zimmerman et al. 1988, Guenther et al. 1996, Helmig et al. 1998, Greenberg et al. 2004, Wiedinmyer et al. 2005, Warneke et al. 2010). (F s -F e )/z = L Daytime mixed layer: Steady state isoprene. No net horizontal advection Fs: isoprene emitted into the boundary layer L: Isoprene reacted with OH F e : Isoprene transported out of the boundary layer L is a simple first order loss rate: k [isoprene] [OH] Surface Top of Boundary Layer z Advance #2: Simultaneous constraints of fluxes and chemistry

4. 4 Airborne eddy covariance direct measure of F 1 and F 2 (F 1 -F 2 )/dz = L Daytime mixed layer: Steady state isoprene. No net horizontal advection F 1 : Flux at height 1 L: Isoprene reacted with OH F 2 : Flux at height 2 Height 1 Height 2 dz L = k [isoprene] [OH] Karl et al. 2010 Advance #2: Simultaneous constraints of fluxes and chemistry We now use this relationship to estimate OH.

5. Issue #1: Bias in driving variables derived from meteorological models Isoprene emission estimates are very sensitive to temperature, solar radiation, soil moisture and landcover. Typical bias in model temperature and solar radiation can overestimate isoprene emission by >30%. Evaluation of isoprene emission models using top down emissions data requires careful attention to these driving variables (including spatial scales).

6. Airborne observations of tropical forest isoprene emissions Alex Guenther, Dasa Gu, Haofei Yu Department of Earth System Science University of California, Irvine CA USA and the GoAmazon science team Conclusions: MEGAN Amazonia isoprene emissions are ~20% lower than observed. Satellite estimates are even lower. Dry season emissions are 2X higher than wet season Airborne observations reveal a previously unrecognized elevational gradient in Amazonia isoprene emissions

7. Method: Airborne eddy covariance using PTRMS Misztal et al. EST in review 1. Fast response isoprene and vertical wind data 2. Calculate flux using wavelet approach with spatial resolution of ~ 2km 3. Adjust for flux divergence between surface and aircraft height

8. Method: Airborne eddy covariance using PTRMS Yu et al. in preparation 4. Calculate “half dome footprint” based on altitude, wind speed and direction Similar results (average isoprene emission for different for vegetation types) for 2km, 4km, and 6km footprints

9. 9 Method: validated in region with distinct isolated isoprene emission sources (California oak woodlands) Misztal et al. EST in review Average flux for 48 California ecosystems r 2 = 0.79 Slope = 1.09

10. Observed Predicted (MEGAN) Wet season 6.2 5.6 Dry Season 12.9 9.04 Longitude Latitude Gu et al. in preparation Shilling et al. PNNL G1 PTRMS data Results: Amazon isoprene emission measured by aircraft and predicted by MEGAN biogenic emission model

11. References Karl, T., A. Guenther, R. J. Yokelson, J. Greenberg, M. Potosnak, D. R. Blake & P. Artaxo (2007) The tropical forest and fire emissions experiment: Emission, chemistry, and transport of biogenic volatile organic compounds in the lower atmosphere over Amazonia. JGR-Atmos., 112, Doi 10.1029/2007jd008539. Karl, T., P. K. Misztal, H. H. Jonsson, S. Shertz, A. H. Goldstein & A. B. Guenther (2013) Airborne flux measurements of BVOCs above Californian oak forests: Experimental investigation of surface and entrainment fluxes, OH densities and Dahmköhler numbers. J. Atmos. Sci., 70, 3277-3287. Misztal, P. K., T. Karl, R. Weber, H. H. Jonsson, A. B. Guenther & A. H. Goldstein (2014) Airborne flux measurements of biogenic isoprene over California. Atmos. Chem. Phys., 14, 10631-10647. Misztal et al. in review Yu et al. in preparation Gu et al. in preparation