Research Programs

Biosphere-Atmosphere Interactions Group ( BAI)
FY2006 activities

TIIMES Theme:
BGS, BEACHON

Research Team: Jim Greenberg-ACD& TIIMES, Alex Guenther-ACD& TIIMES, Peter Harley-ACD& TIIMES, Thomas Karl-ACD& TIIMES, Sou Matsunaga-ACD, Lee Mauldin-ACD, Jim Smith-ACD, Andrew Turnipseed-ACD& TIIMES, Tim VanReken- ACD& MMM, Christine Wiedinmyer- ACD& TIIMES

Collaborators:

Laboratory Studies: Paul Palmer-Cornell University, Jed Sparks-Cornell University

Field Studies: Yoshizumi Kajii & his group-Tokyo Metro University, Maria Papiez-Univ Nevada Desert Research Inst, Mark Potosnak-Univ of Nevada Desert Research Inst., Birgit Wehner-Inst for Tropospheric Res

Modeling: Jeremey Avise-Washington St Univ, Jack Chen-Washington St Univ, Susan Fergusen-US Forest Service, Detlev Helmig-CU, Brian Lamb-Washington St Univ, Cliff Mass-Univ Washington, Jana Milford-CU

Laboratory Studies

1. Methanol and acetone emissions from vegetation.

Methanol and acetone are among the dominant contributors to total Biogenic Volatile Organic Compounds (BVOC) emissions and are important for atmospheric chemistry in some regions. NCAR scientists Peter Harley, Jim Greenberg and Alex Guenther characterized variations in biogenic methanol and acetone emission rates and used the results as the basis of a new numerical model of methanol and acetone emissions. The model is able to simulate most of the observed variations.

2. Response of biogenic isoprene emission to elevated ozone.

Previous NCAR field observations have demonstrated that high isoprene emissions can be induced by short term exposure to elevated ozone concentrations. NCAR scientists Peter Harley, Jim Greenberg and Alex Guenther and visitors Paul Palmer and Jed Sparks (Cornell University) investigated this phenomenon under controlled laboratory conditions. The studies demonstrated that the response of isoprene emission to elevated ozone is negligible in most cases.

3. Biogenic SOA formation and growth.

A new facility for investigating biogenic Secondary Organic Aerosol (SOA) formation and growth was developed in the new NCAR Foothills Laboratory and was successfully used to generate particle formation and growth from vegetation emissions. Tim VanReken, Jim Smith, Peter Harley, Jim Greenberg and Alex Guenther used this facility to conduct initial studies to demonstrate the utility of the facility. The results show that the mixture of compounds emitted from a plant result in SOA production and growth that cannot be explained by observations of the oxidation of individual artificial compounds. A publication describing the facility and initial results is in review.

Field Studies

1. Niwot Ridge 2006 biogenic particle production and growth study.

New particle production and growth has been observed at several remote sites and has been associated with biogenic emissions of Volatile Organic Compounds (VOC). Previous studies in the U.S. have only considered a few biogenic VOC and have had little or no information on aerosol chemical composition. The processes controlling particle production, and even the compounds responsible, are not well understood. NCAR scientists Jim Smith, Lee Mauldin, Jim Greenberg, Thomas Karl, Sou Matsunaga, Andrew Turnipseed, and Alex Guenther collaborated with Birgit Wehner (Institute for Tropospheric Research – Liepzig, Germany) to study particle formation and growth at the University of Colorado Mountain Research Station on Niwot ridge. Particle production and growth events were observed during conditions that brought clean continental air to the site.

2. Hokkaido Japan 2006 OH reactivity study.

Observations of OH and other trace gases at rural and remote sites suggest that OH losses are considerably higher than what can be accounted for by the measured OH sinks. Sou Matsunaga, Alex Guenther and Jim Greenberg collaborated with Prof. Yoshizumi Kajii’s research group in Tokyo Metropolitan University to investigate OH lifetime and sinks in August 2006 at the Tomakomai Experimental Forest in Hokkaido, Japan. Emissions and ambient concentrations of a wide range of biogenic compounds were measured to characterize compounds, including those not measured in previous studies, that contribute to OH loss.

3. Mojave desert 2006 high molecular weight biogenic VOC study:

Isoprene, monoterpenes and sesquiterpenes are all thought to be important contributors to biogenic secondary aerosol formation. Sou Matsunaga and Alex Guenther used a new sampling/analytical technique to measure sesquiterpenes (SQTs) and even larger and heavier compounds (e.g. oxygenated sesquiterpenes and diterpenes). They collaborated with Mark Potosnak and Maria Papiez (U. Nevada Desert Research Institute) to quantify emissions of these compounds from plants growing in the Mojave Desert near Las Vegas, NV in July 2006. Additional measurements were made in Colorado at the NCAR Foothills Lab. greenhouse and at Niwot Ridge. From those experiments, they discovered that compounds heavier than sesquiterpenes are comparable in emission rate to monoterpenes and sesquiteprenes. Efforts to identify these unknown compounds are currently underway but it is likely that they are highly reactive with high aerosols yields (similar to sesquiterpenes) and so have a major impact on tropospheric chemistry.

Model Comparisons

Figure 1. Left panel: (MVK+MAC)/isoprene ratio plotted versus GPS altitude. The black line corresponds to the median and the dotted gray line to the mean for all data. The dashed blue lines represent lower and upper limits of modeled ratios. Right panel: Lower (180 pptv NOx and 30% cloud cover) and upper (320 pptv NOx and 100% cloud cover) limits of modeled OH density plotted as a function of GPS altitude. Red circle is the calculated OH density according to the PBL budget approach. Horizontal blue lines indicate the depth of the cloud layer

4. Chemistry of Aged Plumes of Smoke (CAPOS) 2004 study (Amazon, Brazil).

Tropical landscapes are thought to be responsible for about 80% of global
biogenic VOC emissions and yet are among the least understood. Global chemistry and transport models often perform poorly when using the biogenic VOC emission rates recommended by current emission models. This could be due to uncertainties in emissions but could also be a result of inaccurate characterization of boundary layer meteorology and/or chemistry. Aircraft measurements of biogenic VOC and their oxidation products were used to investigate the ability of photochemical models to predict atmospheric concentrations of OH and other oxidants. The results illustrated in Figure 1 show that a photochemical model underestimates the OH by about a factor of 5 in comparison to a planetary boundary layer (PBL) approach.

Modeling Studies

1. Future Air Quality

Alex Guenther and Christine Wiedinmyer collaborated with Jack Chen, Jeremey Avise, and Brian Lamb (Wash. State U.), Cliff Mass (U. Washington) and Susan Fergusen (US Forest Service) to investigate the impact of future climate and landcover on regional air quality in the Pacific Northwest and NorthCentral U.S. The results indicate that U.S. regional air quality will change even if anthropogenic emissions remain the same. The changes are due to a combination of pollutant transport from other countries emissions, changes in wildfire emissions, and changes in biogenic emissions. A range of future biogenic emission scenarios are being investigated including various land cover change scenarios (i.e. tree plantations, agriculture, and urbanization). Dramatic impacts on regional air quality are predicted for scenarios associated with increases in tree plantations for carbon sequestration.

2. Sesquiterpene SOA

Christine Wiedinmyer and Alex Guenther are working with Jana Milford and Detlev Helmig (University of Colorado) to investigate the contribution of biogenic VOC emissions to secondary organic aerosols (SOA) in the U.S. Initial results indicate that sesquiterpenes, monoterpenes, and isoprene all make a significant contribution to regional SOA production.

Models and Databases for the Scientific Community

1. Model of Emissions of Gases and Aerosols from Nature (MEGAN).

Alex Guenther completed the development of the isoprene component of the MEGAN model and a manuscript describing this model was published and made available to the scientific community on the NCAR data portal. Several efforts are underway to incorporate MEGAN into chemistry and transport model systems including NCAR’s WRF - CHEM and CCSM- CLM and the USEPA’s regulatory models. Improved landcover for the U.S. was incorporated into the model and a method was developed to characterize urban vegetation.

2. North American wildfire emission model.

Christine Wiedinmyer (NCAR-ACD) developed a modeling framework to predict daily emissions from fires for all of North America at a 1km resolution. A manuscript describing the approach was published and has been made available to other researchers and regulatory air quality modelers.