Professor Gordon’s research group is interested in how atmospheric particulate matter influences weather and climate, both directly and by interacting with clouds. Particles in the atmosphere may come from natural or anthropogenic (air pollution) sources. Every cloud droplet in our atmosphere formed around a particle, and so polluted clouds have more droplets in them. Clouds with more droplets are brighter so reflect more light back to the Sun. Therefore atmospheric particles generally cool the climate. However, some particles, usually those that are mainly soot, can absorb solar radiation and heat clouds up, causing them to evaporate, and this leads to a warming effect because clouds are more reflective than Earth’s surface below them. Particles in the atmosphere also lead to reduced visibility, either as haze or by influencing the properties of fog. It is therefore important for aviation weather forecasts to account for particle concentrations. Finally, particles can also affect precipitation in clouds containing ice, leading to further complicated weather and climate effects. To understand atmospheric particles and their effects, we run simulations with the UK Met Office “Unified Model,” which is used for both weather forecasting and climate prediction. Our research requires adding new code to the model to better represent both particles and clouds.
Hamish Gordon is an assistant research professor with the Engineering Research Accelerator and the Center for Atmospheric Particle Studies. His research interests are focused on the effects of air pollution and natural airborne particles on clouds and climate. He received his first degree from the University of Cambridge in 2009, and his doctorate from the University of Oxford in experimental high energy physics in 2013. He moved to Carnegie Mellon from a postdoc position at the University of Leeds in 2019.
To study the climate effects of atmospheric particles (the focus of the video featuring Professor Gordon, linked below), we are playing a leading role in the development of the double-moment microphysics configuration of the Unified Model, in which both aerosol and cloud particle mass and particle number concentrations are tracked separately. We make extensive use of atmospheric observations (made at the surface, from aircraft, or from satellites in space) to validate and improve our simulations. Professor Gordon was part of a large team observing clouds in the south-east Atlantic using the UK research aircraft, based at Ascension Island in 2017. The smoke aerosols mixing into clouds can be seen on a day of the measurement campaign in the figure opposite, taken by the MODIS instrument on the TERRA satellite.
Our group is also interested in how aerosols affect the weather. By scattering and absorbing radiation and changing the properties of clouds, atmospheric particles can strongly affect visibility, as well as Earth’s climate. Professor Gordon is starting collaborations with various researchers studying aerosol effects on visibility using the UK Met Office Unified Model, including some at Delhi’s National Center for Medium Range Weather Forecasting. An example of low visibility in Delhi is pictured. We will update this page as the research progresses.
Professor Gordon’s research in atmospheric science started at the CLOUD experiment at CERN, and his group plays a leading role in understanding the influence of secondary aerosol formation (essentially, gas molecules in the atmosphere sticking together to make particles) on Earth’s climate. The CLOUD chamber at CERN, shown here, is the world’s leading laboratory experiment for aerosol formation studies. The primary aim of the experiment is to measure the rate at which new particle formation occurs from carefully controlled gas mixtures in ultra-clean conditions. The rates are then parameterized and included into atmospheric models to represent the effects of this process on climate and air quality. Professor Gordon was involved in this research while working first at CERN and then at the University of Leeds. We are now funded by the NASA Roses program to continue studying the implications of new aerosol formation for the atmosphere, working in the Center for Atmospheric Particle Studies at CMU with Professor Neil Donahue.
- H. Gordon et al, Development of aerosol activation in the double-moment Unified Model and evaluation with CLARIFY measurements, Atmospheric Chemistry and Physics, 20 10997 (2020)
- H. Gordon, P. R. Field, S. J. Abel, M. Dalvi, D. P. Grosvenor, et al. Large simulated radiative effects of smoke in the south-east Atlantic. Atmospheric Chemistry and Physics, 18(20): 15261-15289, 2018
- H. Gordon, J. Kirkby, U. Baltensperger, F. Bianchi, M. Breitenlechner, et al. Causes and importance of new particle formation in the present-day and preindustrial atmospheres. Journal of Geophysical Research: Atmospheres, 122(16):8739-8760, 2017
- E. M. Dunne, H. Gordon, A. Kuerten, J. Almeida, J. Duplissy, et al. Global atmospheric particle formation from CERN CLOUD measurements. Science, 354:1119-1124, 2016
- H. Gordon, K. Sengupta, A. Rap, J. Duplissy, C. Frege, et al. Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation. Proceedings of the National Academy of Sciences, 113:12053-12058, 2016
- J. Trostl, W. K. Chuang, H. Gordon, M. Heinritzi, et al. The role of low-volatility organic compounds in initial particle growth in the atmosphere. Nature, 533(7604):527-531, 2016
- R. Aaij …H. Gordon et al, (the LHCb Collaboration), Search for CP violation in D+->phipi+ and D+->K0Spi decays. JHEP, 1306:112, 2013
- R. Aaij … H. Gordon et al. (the LHCb Collaboration), Measurement of the D+production asymmetry in 7 TeV pp collisions. Phys. Lett., B718, 2013
- R. Aaij… H.Gordon et al. (the LHCb Collaboration), Search for CP violation in D+->K-K+pi+ decays. Phys. Rev., D84: 112008, 2011
- Y. Shinozuka…H.Gordon et al, Modeling the smoky troposphere of the southeast Atlantic: a comparison to ORACLES airborne observations from September of 2016, Atmospheric Chemistry and Physics, 2020
- Zhao, M. Shrivastava, N. Donahue, H. Gordon et al, High concentration of ultrafine particles in the Amazon free troposphere produced by organic new particle formation, Proc. Natl Acad. Sci. (2020)
- Weber, … H.Gordon et al, CRI-HOM: A novel mechanism for simulating Highly Oxygenated Organic Molecules (HOMs) in global chemistry-aerosol-climate models, Atmospheric Chemistry and Physics, 20 10889 (2020)
- Simon, .. H.Gordon et al, Molecular understanding of new-particle formation from alpha-pinene between −50 °C and 25 °C. Atmospheric Chemistry and Physics, 20 9193 (2020)
- I. McCoy, D. McCoy,…and H. Gordon, The hemispheric contrast in cloud microphysical properties constrains aerosol forcing, Proc. Natl. Acad. Sci. (2020)
- D. Stolzenburg, M. Simon, A. Ranjithkumar, A. Kürten, K. Lehtipalo, H. Gordon, et al, Enhanced growth rate of atmospheric particles from sulfuric acid, Atmospheric Chemistry and Physics, 2020
- C. Yan, … H. Gordon et al, Size-dependent influence of NOx on the growth rates of organic aerosol particles, Science Advances 6 22 (2020)
- D. McCoy, P. Field, H. Gordon, G. S. Elsaesser, and D. P. Grosvenor, Untangling causality in midlatitude aerosol-cloud adjustments, Atmospheric Chemistry and Physics (2020)
- A. Ranjithkumar, H. Gordon et al, Constraints on global aerosol number concentration, SO2 and condensation sink in UKESM1 using ATom measurements, Atmospheric Chemistry and Physics Discussions, 2020
- J. Haywood …. H. Gordon et al, Overview: the Cloud Aerosol Radiation Interaction and Forcing: Year 2017 (CLARIFY-2017) measurement campaign, Atmospheric Chemistry and Physics Discussions (2020)
- H. Che, P. Stier, H. Gordon, D. Watson-Parris and L. Deaconu, The significant role of biomass burning aerosols in clouds and radiation in the South-east Atlantic Ocean, Atmospheric Chemistry and Physics Discussions, 2020
- M. Heinritzi, …, H. Gordon, et al, Molecular understanding of the suppression of new-particle formation by isoprene, Atmospheric Chemistry and Physics Discussions, 2020 (accepted)