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I am a postdoctoral research fellow in the Atmospheric Chemistry Modeling Group at Harvard University under the supervision of Jennifer Logan.Our group aims to understand the abundance of air pollutants and greenhouse gases in the atmosphere by examining their natural and man-made sources, chemical fate in the atmosphere, and transport on global and regional scales.

For this work we make use of surface, aircraft and satellite measurements interpreted with three-dimensional models of tropospheric chemistry (GEOS-Chem, GCAP, GISS). Details on my research interests are listed below.

CHEMISTRY-CLIMATE INTERACTIONS

EFFECTS OF CLIMATE CHANGE ON NORTH AMERICAN FOREST FIRE EMISSIONS AND IMPACT ON U.S. AIR QUALITY

Recent work suggests that wild fires over North America have increased in duration, frequency, and intensity and that further increases in temperature are expected over the next few decades potentially driving further increases in wild fire. For my postdoctoral work, I am investigating the effects of North American fires on U.S. ozone air quality under various climate change scenarios.This involves the following:

  1. Quantifying the effects of present day fires using a global 3-D chemical transport model (CTM) driven by assimilated meteorology constrained with surface aircraft observations (ICARTT, POLARCAT/ARCTAS), Validating burning emission estimates (2000-2050) for United States and Canada developed by Spracklen et al., [2007], in preparation, with (1), and
  2. Conducting simulations of aerosol and chemistry in a future climate using a CTM driven by output from the NASA/GISS General Circulation Model (GCM).

This project will provide a first-ever assessment of the effects of fires in a future climate on air quality over the entire United States.

Co-investigators: Dominick Spracklen, Jennifer Logan (Postdoctoral Advisor), Loretta Mickley

For more information: Seventh Symposium on Fire and Forest Meteorology, October 23, 2007, Bar Harbor, Maine , “Effects of climate change on forest fires over North America and impact on U.S. air quality and visibility ”. [ppt]

EMISSIONS MAPPING

BIOGENIC vs. ANTHROPOGENIC SOURCES OF CO OVER THE UNITED STATES

  

Extensive aircraft mapping of the U.S. boundary layer in summer 2004 during ICARTT confirms the recent decrease NOx emissions required by recent regulation, and reveals a large overestimate of carbon monoxide (CO) emissions in current inventories.

For full details see Hudman, et al. [2008]

 

Further support for large CO overestimate in current U.S. inventory:

Miller, S. M., D. M. Matross, A. E. Andrews,... R. C. Hudman, ... Sources of carbon monoxide and formaldehyde in North America determined from high resolution atmospheric data, Atmos. Chem. Phys., submitted.

NOx emissions over the United States:

Hudman, R. C., D. J. Jacob, S. Turquety, E. M. Leibensperger, L. T. Murray, S. Wu, A. B. Gilliland, M. Avery, T. H. Bertram, W. Brune, R. C. Cohen, J. E. Dibb, F. M. Flocke, A. Fried, J. Holloway, J. A. Neuman, R. Orville, A. Perring, X. Ren, T. B. Ryerson, G. W. Sachse, H. B. Singh, A. Swanson, P. J. Wooldridge (2006), Surface and lightning sources of nitrogen oxides over the United States: magnitudes, chemical evolution, and outflow, J. Geophys. Res., 112, D12S05, doi:10.1029/2006JD007912. [PDF]


TROPOSPHERIC COMPOSITION

LIGHTNING NOx OVER THE UNITED STATES AND IMPACT ON TROPOSPHERIC OZONE

 

We find NOx in the upper troposphere is largely understimated in GEOS-Chem over the United States during the summer, reflecting a higher-than-expected (factor of four) lightning source. This lightning source drives in turn a large ozone enhancement in the upper troposphere (>10 ppbv) with implications for radiative forcing and climate feedback through changes in lightning.

For full details see Hudman et al., [2007]

 

NORTH AMERICAN INFLUENCE ON TROPOSPHERIC OZONE

  

We use ICARTT constraints on North American NOx emissions (0.72 Tg N fossil fuel, 0.32 Tg N biomass burning, 0.28 Tg N lightning for July 1 – August 15) to derive new estimates of the summertime North American impact on tropospheric ozone. We find NOx emissions increased the hemispheric tropospheric ozone burden by 14%, with comparable contributions from fossil fuel and lightning (5-6%) and 3% contribution from biomass burning. Uncharacteristically high wildfires in Alaska and Canada enhanced mean surface ozone over Western Europe by 3-5 ppbv, comparable to the contribution from North American fossil fuel.

For full details see Hudman et al., [2008b]

 

Collaborations using GEOS-Chem to interpret ICARTT observations:

Liang, Q., L. Jaeglé, R. C. Hudman , S. Turquety, D. J. Jacob, M. A. Avery, E.V. Browell, G. W. Sachse, D. R. Blake, W. Brune, X. Ren, R. C. Cohen, J. E. Dibb, A.Fried, H. Fuelberg, M. Porter, B. G. Heikes, G. Huey, H. B. Singh, P. O. Wennberg (2007), Summertime influence of Asian pollution in the free troposphere over North America, J. Geophys. Res. , 112, D12S11, doi:10.1029/2006JD007919. [PDF]

Singh, H. B., L. Salas, D. Herlth, R. Kolyer, E. Czech, M. Avery, J. H. Crawford, G. W. Sachse, D. R. Blake, R. C. Cohen, J. Dibb, G. Huey, R. C. Hudman , D. J. Jacob, L. K. Emmons, L. W. Horowitz, F. Flocke, Y. Tang, G. R. Carmichael (2007), Reactive Nitrogen Distribution and Partitioning in the North American Troposphere and Lowermost Stratosphere, J. Geophys. Res. , 112 , D12S04 , doi: 10.1029/2006JD007664 .

Turquety, S., J.A. Logan, D.J. Jacob, R.C. Hudman, F.Y. Leung, C.L. Heald, R. M. Yantosca, S. Wu, L. K. Emmons, D.P. Edwards, and G.W. Sachse (2007), Inventory of boreal fire emissions for North America in 2004: the importance of peat burning and pyro-convective injection, J. Geophys. Res.,112, D12S03, doi:10.1029/2006JD007281. [PDF]

Heald, C.L., D.J. Jacob, S. Turquety, R.C. Hudman, R.J. Weber, A.P. Sullivan, R.E. Peltier, E.L. Atlas, J.A. de Gouw, C. Warneke, J.S. Holloway, J.A. Neuman, F.M. Flocke, and J.H. Seinfeld (2007), Concentrations and sources of organic carbon aerosol in the free troposphere over North America, J. Geophys. Res., D14310, doi:10.1029/2005JD006847. [PDF]

Zhang, L., D. J. Jacob, K. W. Bowman, J. A. Logan, S. Turquety, R. C. Hudman, Q. Li, R. Beer, H. M. Worden, J. R. Worden, C. P. Rinsland, S. S. Kulawik, M. C. Lampel, M. W. Shephard, B. M. Fisher, A. Eldering, and M. A. Avery (2006), Continental outflow of ozone pollution as determined by Ozone-CO correlations from the TES satellite instrument, Geophys. Res. Lett.,33, L18804, doi:10.1029/2006GL026399. [PDF]

Millet, D.B., A.H. Goldstein, R. Holzinger, B. Williams, J.D. Allan, J.-L. Jimenez, D.R. Worsnop, J.M. Roberts, A.B. White, R.C. Hudman, I.T. Bertschi, and A. Stohl (2006), Chemical characteristics of North American surface-layer outflow: Insights from Chebogue Point, J. Geophys. Res., doi:10.1029/2006JD007287. [PDF]

Millet, D.B., D.J. Jacob, S. Turquety, R.C. Hudman, S. Wu, A. Fried, J. Walega, B.G. Heikes, D.R. Blake, H.B. Singh, B.E. Anderson, and A.D. Clarke (2006), Formaldehyde distribution over North America: Implications for satellite retrievals of formaldehyde columns and isoprene emission, J. Geophys. Res., doi:10.1029/2005JD006853. [PDF]

Li, Q.B., D.J. Jacob, R. Park, Y.X. Wang, C.L. Heald, R. C. Hudman , R.M. Yantosca, R.V. Martin, and M.J. Evans (2005), North American pollution outflow and the trapping of convectively lifted pollution by upper-level anticyclone, J. Geophys. Res., 110,D10301. [PDF]

INTERCONTINENTAL TRANSPORT AND TRANSFORMATION OF POLLUTION

EFFECTS OF ASIAN POLLUTION ON U.S. OZONE AIR QUALITY

We used GEOS-Chem to interpret the ITCT 2K2 and PEACE-B observations in terms of ozone production during transpacific transport of Asian pollution, and to assess the implications for surface ozone air quality in the United States . We found Peroxyacetyl nitrate (PAN) decomposition to represent a major and possibly dominant component of the ozone enhancement in transpacific Asian pollution plumes. Strong dilution of Asian pollution plumes takes place during entrainment in the U.S. boundary layer, greatly reducing their impact at U.S. surface sites. California mountain sites are more sensitive to Asian pollution because of their exposure to the free troposphere.

For full details see Hudman et al., [2004]

More on Asian outflow and transpacific inflow:

Kondo, Y., K. Nakamura, R. C. Hudman, G. Chen, Y. Miyazaki, N. Takegawa, M. Koike, M. Ko, K. Kita, D. R. Blake, T. Shirai, S. Kawakami (2008), Mechanisms that influence the formation of high-ozone regions in the boundary layer downwind of the Asian continent in winter and spring, J. Geophys. Res., 113, D15304, doi:10.1029/2007JD008978.

Goldstein, A.H., D.B. Millet, M. McKay, L. Jaegle, L. Horowitz, O. Cooper, R. Hudman, D.J. Jacob, S. Oltmans, and A. Clark (2004), Impact of Asian emissions on observations at Trinidad Head, California, during ITCT 2K2, J. Geophys. Res., 109, D23S17. [PDF]

Other Collaborations

Data Assimilation:

Stajner, I, K. Wargan, S. Pawson, …, R. C. Hudman , ... (2008), Assimilated Ozone from EOS-Aura: Evaluation of the Tropopause Region and Tropospheric Columns, J. Geophys. Res., 113, D16S32, doi:10.1029/2007JD008863.

Cloud Chemistry:

Barth M. C., S. Sillman, R. Hudman , M. Z. Jacobson, C.H. Kim , A. Monod, and J. Liang (2003), Summary of the cloud chemistry modeling intercomparison: Photochemical box model simulation. J. Geophys. Res., 108(D7) 4214.