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Current scientific projects

CHEEREIO: An open-source tool for chemical data assimilation

The GEOS-Chem CHEmistry and Emissions REanalysis Interface with Observations (CHEEREIO) is a set of Python and shell scripts that support data assimilation and emissions inversions for arbitrary runs of the GEOS-Chem chemical transport model via an ensemble approach (i.e. without the model adjoint). Code and documentation are available on Github and ReadTheDocs. CHEEREIO follows five design principles:

CHEEREIO can be used out-of-the-box for nonlinear multiconstuent data assimilation (e.g. using satellite and surface NO2 and O3 for joint assimilation of NOx/O3 concentration fields and NOx emissions). Emissions scaling factors can be separated by source (e.g. agriculture optimized separately from oil and gas).

CHEEREIO is currently under development. A relatively stable version should be available in early 2022.

CHEEREIO workflow diagram

Figure: The CHEEREIO code workflow.

Emissions and concentrations of pollutants in China

Pollutants like tropospheric ozone and fine particulate matter (PM2.5) cause serious public health burdens, especially in eastern China. In response to the severe smog problems, the Chinese government implemented the Action Plan on Air Pollution Prevention and Control in 2013. The plan led to rapid reductions in emissions of ozone precursors like NOx and aerosol precursors like SO2. However, observations show that while PM2.5 has decreased, surface ozone has increased, even though emissions have fallen. This project seeks to understand the PM2.5/ozone tradeoff both in the present day and under various models of the future.

China air quality map

Figure: Air quality changes due to strong NTCF emission reductions in China by midcentury (2045-54); PM2.5 is projected to improve due to modeled emissions mitigation while ozone is projected to worsen.

Associated publications and presentations

Pendergrass, D. C., L.W. Horowitz, and V. Naik. Modeling impact of strong regulation of near-term climate forcers in China on mid-21st century air quality and climate using the GFDL-ESM4 coupled model. American Geophysical Union Fall Meeting, San Francisco, Calif., December 13, 2019. Talk. Slides.

Using machine learning and satellite data to map fine particulate matter pollution in east Asia

Fine particulate matter (PM2.5) is an air pollutant associated with millions of deaths per year. Measurements of this pollutant are made at surface sites throughout east Asia, but the vast majority of surface area has no available measurements. This means that we can't fully evaluate the impact PM2.5 has on public health, nor do we have a fully view of the atmospheric state of this region. Satellites offer a solution since they image a wide area at once. A geostationary satellite instrument called GOCI has been imaging east Asia 8 times per day. One of the measurements GOCI takes is called Aerosol Optical Depth (AOD), which is a measure of the transparency of the atmosphere. AOD is related to surface PM2.5 but the relationship is complicated; for example, the satellite measures a column of air all at once, and it cannot tell if pollution is high in the sky or on the ground, where humans can inhale it. This project uses a machine learning algorithm called a random forest to link AOD, meteorology, and other data to measured surface PM2.5 in east Asia. The result is a high-resolution, daily dataset that can be used for studies of epidemiology and atmospheric chemistry.

Beijing pollution event zoomed

Figure: Daily PM2.5 concentrations during a pollution event in the North China Plain, around Beijing (December 16-21, 2016). Predictions from the random forest algorithm (background, on 6x6 km2 grid scale) are compared to observations made on the ground (circles). We see that the model is able to reproduce even this extreme level of pollution.

Associated publications and presentations

Pendergrass, D. C., D. J. Jacob, S. Zhai, J. Kim, J-H. Koo, S. Lee, M. Bae, and S. Kim. (2021). Continuous mapping of fine particulate matter (PM2.5) air quality in East Asia at daily 6x6 km2 resolution by application of a random forest algorithm to 2011-2019 GOCI geostationary satellite data. Under review at Atmospheric Measurement Techniques. PDF. Publisher's preprint. Associated dataset available from Dataverse.

Pendergrass, D. C., D. J. Jacob, S. Zhai, J. Kim, J-H. Koo, M. Bae, and S. Kim. Continuous Mapping of Fine Particulate Matter (PM2.5) Air Quality in East Asia by Application of a Random Forest Algorithm to GOCI Geostationary Satellite Data. American Geophysical Union Fall Meeting, New Orleans, La., December 2021. Submitted.

Other current projects



I was on the staff of Harvard Magazine, and I freelance for a variety of outlets, including Harper's and The Guardian. Some of my articles are linked here.

Half-Earth Socialism

A book from Verso, co-authored with environmental historian Troy Vettese, on how we can get out of our current ecological mess. Due out April 2022. You can order it from the publisher here.

Half-earth socialism cover

Commonplace Book

John Locke advised that his readers keep a commonplace book, a document where quotes, proverbs, and ideas would be gathered in an unrestricted way. This is my commonplace book. It is full of quotes and ideas that I find compelling and continue to return to.

Log on wheels

A hot new startup that sells logs on wheels for personal transporation.

Musical Composition

I am a composer of modern and experimental music. You can learn more about my compositions on my music website and you can listen to my works on my SoundCloud.

Archived science projects

Extreme value theory applied to environmental science

Extreme value theory is a branch of statistics dedicated to the analysis of outliers and rare events. In environmental science, extremes are sometimes more important than measures of central tendency: for example, bridge builders care more about the maximum height of a river than its mean height. I've used extreme value theory to link winter meteorology in Beijing to severe smog events, which can shut down the city and are a major threat to public health. If you are interested in using this methodology in your own research, send me an email (drew@drewpendergrass.com) and we can collaborate.

GRL EVT plot

Figure: Probability (given in colored contours) for PM2.5 in Beijing to exceed 300 μg m-3 given relative humidity and 850-hPa meridional winds. Actual observations are overlaid on top: green dots represent days that exceeded 300 μg m-3, and black dots represent the rest.

Associated publications and presentations

Pendergrass, D. C., Shen, L., Jacob, D. J., & Mickley, L. J. (2019). Predicting the Impact of Climate Change on Severe Wintertime Particulate Pollution Events in Beijing Using Extreme Value Theory. Geophysical Research Letters, 46(3), 1824–1830. Publisher's version. PDF.

Pendergrass, D. C., L. Shen, D. J. Jacob, and L. J. Mickley. Predicting the impact of climate change on severe winter haze pollution events in Beijing using extreme value theory. American Geophysical Union Fall Meeting, Washington D.C., December 11, 2018. Talk. Slides.

Other archived projects


Alchemy is a single-player military strategy game written in Java. It makes liberal use of statistical analysis of maps and resource distributions to make the goal of world domination as fair as possible. Alchemy is highly efficient and is designed to run on virtually any modern computer - more is on the game's website here.

Alchemy box cover

Radcliffe Research Partner for Anthony Tan

For the 2016-17 academic year, I wrote code, processed and edited recordings, and typeset music for Anthony Tan at the Radcliffe Institute for Advanced Study. This culminated in a May 2017 concert, where I was a performer.

Intonation, Harmonics and Timbre notes

This is a resource on the physics of sound and musical instruments, which I wrote as I was researching the science behind my tuning software. You can read more on the IHT homepage.