University of Houston
Natural Sciences and Mathematics
Department of Earth and Atmospheric Sciences

  • EPA
  • HARC
  • NASA
  • NSF
  • TCEQ
  • EDF
  Atmospheric Mecury group

Atmospheric Mercury

Our mercury research group is led by Drs. Talbot (rtalbot@uh.edu) and Mao (hmao@esf.edu).   Dr. Talbot is at the University of Houston (UH) and Dr. Mao is at the SUNY-College of Environmental Science & Forestry (ESF).

  • Research Group
  • Goal
  • Results
  • Publications
University Of Houston

Robert Talbot - Professor of Atmospheric Chemistry
Patrick Laine – Postdoctoral Fellow (mercury measurements)
Xin (Lindsay) Lan – Ph.D. Student (regional modeling)
Dara Feddersen – Ph.D. Student (mercury measurements)
Azucean Torres - M.S Student (mercury measurements)

SUNY - College of Environmental Science & Forestry (ESF).

Huiting Mao – Associate Professor of Environmental Chemistry
Casey Hall – Ph.D. Student (mercury measurements)
Zhuyun Ye – Ph.D. Student (mercury modeling)

  1. To understand the sources, sinks, and chemical transformations of atmospheric mercury on regional-to-global scales.
  2. Improve the analytical methodologies for measuring atmospheric mercury.
  3. Improve emission inventories for mercury.
  4. Improve simulations of mercury with the 3-d regional model CMAQ.

We started measuring atmospheric mercury in 2003 at Thompson Farm in New Hampshire.  The site is still operating today with funding from EPA.  It is a site (NH06) in the Atmospheric Mercury Network (AMNet).  Information on this program can be found here http://nadp.sws.uiuc.edu/amn/.  We now also operate measurement sites in Syracuse, NY and Houston, TX.

  • We have developed our own custom box model for studying chemical transformations of atmospheric mercury.
  • We have fabricated a custom instrument to measure mercury with one minute time response.
  • We were one of the first groups to measure mercury from an airborne platform.

Mercury is a serious environmental toxin that is distributed globally by large-scale atmospheric circulations.  In the atmosphere mercury exists in diverse chemical forms that are comprised of gaseous elemental mercury (Hgo), reactive gaseous mercury (RGM = HgCl2 + HgBr2 + HgOBr +. . .), and particulate-phase mercury (HgP).  Near the Earth’s surface Hgo is observed ubiquitously with contemporary mixing ratios at the several hundred parts per quadrillion (ppqv) level, with RGM and HgP comprising only a few percent of the total mercury.

Units:  1 ng m-3 = 112 ppqv = 3 × 106 molecules cm-3 of Hgo

The global chemical transformations we are studying are depicted in the figure below.  The uncertainties are numerous.  The Houston area in particular has numerous large sources of atmospheric mercury.  We would like to develop chemical fingerprints of specific sources using stable Hg isotopes.  We hope to do this using a small aircraft to sample individual plumes.  We also hope to develop a methodology for measuring individual RGM species using chemical ionization mass spectrometry (CIMS).

Our research has shown that:

  • Hgo is depleted to zero in the stratosphere.


  • Hgo is depleted to near zero near the surface over the Arctic Ocean in springtime and it is related to the occurrence of atomic halogens.
  • Hgo has strong seasonality with the lowest mixing ratios in early fall and highest in early spring.


  • The seasonality in Hgo is consistent across large portions of the U.S.
  • In rural locations Hgo exhibits a strong diurnal cycle with the lowest mixing ratios in early morning.


  • Over the ocean, RGM is highest in midday, and lowest at night while Hgo exhibits the opposite pattern.
  • In summer HgP is associated primarily with coarse (>1µm) aerosols, but in winter this switches to the fine fraction (<1µm).


  • HgP is not removed from the atmosphere efficiently by snow.
  • Hgo exhibits strong correlation with carbon monoxide (CO), especially in wintertime.


  • The diurnal cycle of Hgo is facilitated greatly by uptake in the water layer of aerosols and dissolution into dew on Earth’s surfaces.
  • The Houston area experiences large and numerous excursions above the Northern Hemispheric background level of ~160 ppqv.


  • RGM is not a “sticky” gas.  In fact, it’s very difficult to remove from an ambient air stream.

Lan, X., and R. Talbot (2011), Seasonal and annual variations of atmospheric mercury across the U.S. determined from AMNet monitoring data, Atmos. Chem. Phys., in preparation.

Feddersen, D., R. Talbot, H. Mao, M. A. S. Lombard, and B Sive (2011), Aerosol size distribution of atmospheric mercury in marine and continental atmospheres, Atmosphere, in preparation.

Kim, S. Y., R. Talbot, and H. Mao (2011), Cycling of elemental mercury: Importance of water vapor, Geophys Res. Lett., submitted.

Mao, H., and R. Talbot (2011), Long-term variation in speciated mercury at marine, coastal and inland sites in New England: Part I Temporal Variability, Atmos. Chem. Phys., submitted.

Mao, H., R. Talbot, J. Hegarty, and J. Koermer (2011), Long-term variation in speciated mercury at marine, coastal and inland sites in New England: Part II Relationships with Atmospheric Physical Parameters, Atmos. Chem. Phys. Discuss., 11, 28395-28443.

Lombard, M. A. S., J. G. Bryce, H. Mao, and R. Talbot (2011), Mercury deposition in Southern New Hampshire, 2006–2009, Atmos. Chem. Phys., 11, 7657-7668.

Mao, H., R. Talbot, B. Sive, Su Youn Kim, D. R. Blake, and A. J. Weinheimer (2011), Arctic mercury depletion and its quantitative link with halogens, J. Atmos. Chem., DOI: 10.1007/s10874-011-9186-1.

Talbot, R., H. Mao, D. Feddersen, M. Smith, S. Y. Kim, B Sive, K. Haase, and J. Ambrose, Y. Zhou, and R. Russo (2011), Assessment of particulate mercury measured with the manual and automated methods, Atmosphere, 2(1), 1-20; doi:10.3390/atmos2010001.

Kim, Su-Youn, R. Talbot, and H. Mao (2010), Chemical transformations of Hg° during Arctic mercury depletion events sampled from the NASA DC-8,Atmos. Chem. Phys. Discuss., 10, 10077–10112.

Sigler, J. M., H. Mao, B. Sive, and R. Talbot (2009), Oceanic influence on atmospheric mercury at coastal and inland sites: A springtime nor’easter in New England, Atmos. Chem. Phys.9, 4023-4030.

Sigler, J. M., H. Mao, B. Sive, and R. Talbot (2008), Gaseous elemental and reactive mercury in southern New Hampshire, Atmos. Chem. Phys., 9, 1929-1942.

Talbot, R., H. Mao, E. Scheuer, J. Dibb, M. Avery, E. Browell, G. Sachse, S. Vay, D. Blake, G. Huey, and H. Fuelberg (2008), Factors influencing the large-scale distribution of Hg° in the Mexico City area and over the north Pacific, Atmos. Chem. Phys., 8, 2103-2114.
Mao, H., R. Talbot, J. M. Sigler, B. C. Sive, and J. D. Hegarty (2008), Seasonal and diurnal variations of Hg° over New England, Atmos. Chem. Phys., 8, 1403-1421.

Talbot, R., H. Mao, E. Scheuer, J. Dibb, and M. Avery (2007), Total depletion of Hg° in the upper troposphere – lower stratosphere, Geophys. Res. Lett., 34, L23804, doi:10.1029/2007GL031366.