TEAMPACCC
Trends in Earth's Atmospheric Makeup: Pollution of the Air - Chemistry - Climate Connections
Air Pollution
We aim to quantify the sensitivity of ground-level ozone and particle pollution to precursor emissions and chemistry. Ozone and particulates in surface air in many locations reflect a balance of production from local-to-regional anthropogenic and natural sources and of transport. Knowing the ‘break-down’ of sources contributing to air pollution is needed to set attainable standards and to implement effective pollution control policies. Much of our work has focused on U.S. or global air pollution, with some applications over India.
Air quality and health applications of satellite data
Surface ozone sensitivity to precursor emissions: Views from space
While NOx reductions generally lower the overall ozone produced regionally or globally (a ‘NOx-sensitive’ ozone formation regime), urban areas with high NOx levels may benefit from VOC emission control (NOx-saturated regime). We build on prior work using satellite observations of the tropospheric column ratio of HCHO (an intermediate product of VOC oxidation which can serve as a proxy for these emissions) to NO2 (a proxy for NOx ; NOx = NO + NO ) as an indicator for ozone-forming chemistry. We first conducted a model-centric evaluation of uncertainty in using this column-based satellite indicator for surface ozone formation regimes in northern mid-latitude source regions and demonstrated a transition to increasing NOx-sensitivity during the warm season over several northern mid-latitude urban areas as controls on anthropogenic NOx emission controls were implemented from 2005 to 2015 ( Jin et al., 2017 ; see also 11/7/17 NASA image of the day). A new approach to harmonize multi-satellite retrievals (using the consistently retrieved European QA4ECV products) produced a two-decade record of this HCHO/NO2 satellite indicator. This record revealed trends in this satellite indicator correspond to patterns of ground-level ozone changes known to be associated with transitions from NOx-saturated to NOx-sensitive ozone formation ( Jin et al., 2020 ). [NASA fellowship to Xiaomeng Jin, NASA ACMAP & HAQAST].
Tao et al. (2022) used observations from two field campaigns during summer 2018 alongside satellite data plus high-resolution CMAQ simulations to show that both HCHO and NO2 increase, but overall ozone-forming chemistry diagnosed with the ratio of HCHO to NO2, shifts towards higher NOx-sensitivity on days when the ozone NAAQS is exceeded over the New York City and Baltimore/Washington DC areas (see Figure). [NASA HAQAST].
Diurnal variability of air pollutants at the surface and in the column
at the Northeast States for Coordinated Air Use Management (NESCAUM) to infer anthropogenic versus biogenic emission influences based on their characteristic diurnal cycles. Relevant to the interpretation of retrievals from geostationary satellites, we find that column and surface diurnal patterns differ (see Figure to the right), as also found in earlier work. [NASA HAQAST]
Tao et al. (2025) examine diurnal patterns of HCHO and NO2 concentrations across seven sites along a transect stretching from the southwest of New York City (NYC) to Long Island Sound during June-August 2018. We use surface observations, retrievals from Pandora spectrometers, and the Weather Research and Forecasting model coupled with the Community Multiscale Air Quality Model (WRF-CMAQ) simulations (1.33 km horizontal resolution) conducted by collaborators
Ongoing work includes using a variable-resolution chemical transport model over the contiguous U.S. (~14 km over CONUS, MUSICAv0) to evaluate how the temporal resolution of anthropogenic emissions affects diurnal variability in surface and column air pollutants (Tao et al., in review). We uncovered an unexpected sensitivity when switching from daily to hourly NO emissions, which produces contrasting west-east and urban-rural responses in surface NOx and O3, with column NO2 closely tracking surface changes. Monthly-mean impacts are comparable to a uniform 30% NO reduction but are spatially distinct due to local emissions timing and meteorology.
We are also examining diurnal column variations during early-season versus mid-summer high-O3 events in the Northeastern U.S. in 2024, the first full ozone season with hourly daytime retrievals from Tropospheric Emissions: Monitoring of Pollution (TEMPO) (Tao et al., in prep.).
Climate-air quality-health nexus
Cleaner air over New York State
We have examined uncertainties in using satellite aerosol optical depth products to estimate surface fine particulate matter (PM2.5 ) over the Northeastern U.S.A. ( Jin et al., 2019a ) and compared multiple publicly available PM2.5 products to document public health benefits associated with cleaner air across New York State ( Jin et al., 2019b ). We also contributed to technical guidance documents for incorporating satellite data into State Implementation Plans, which are part of the process by which non-attainment areas demonstrate how they will achieve compliance with the National Ambient Air Quality Standards. [NYSERDA, NASA HAQAST]
Interpreting ozone chemistry in wildfire smoke plumes
Smoke impact on tropospheric ozone is substantial, but both physical and chemical variability pose challenges to forecasting local impacts and quantifying wildfire influence on regional and global burdens (Palmo et al. 2025). Understanding ozone formation in smoke plumes in the face of this variability is essential for assessing the local and global impact of fires on ozone, especially as wildfires become more frequent and intense. Air managers need to disentangle natural and anthropogenic sources of ozone to discern the most effective approach to reducing tropospheric ozone. We use satellite measurements of atmospheric composition — formaldehyde (HCHO) and nitrogen dioxide (NO2) — to track the chemistry within smoke plumes as they age and disperse. Using a space-based framework, we estimate ozone formation regime evolution and explore strategies for estimating ozone production rates.
Air pollution distributions and trends
Background ozone over the U.S.A.
We have completed several studies quantifying different aspects of “background” ozone in surface air. We are particularly interested in variability on daily to decadal time scales in the individual components contributing to background (i.e., ozone produced from global methane, from international anthropogenic emissions, from natural biogenic and soil emissions or lightning NOx , and transported from the stratosphere). For example, check out Guo et al. (2018) to see how we used a suite of sensitivity simulations in the GEOS-Chem global chemistry transport model to estimate the influence from individual background sources versus U.S. anthropogenic sources on total surface ozone over 10 continental US regions from 2004 to 2012. We found that the model attributes interannual variability in U.S. background ozone on days when the highest ground-level ozone concentrations were measured to natural sources, not
international pollution transport. [EPA, NASA AQAST]
Changing Air Pollution Extremes
Changes in regional NOx emissions as well as regional climate are expected to alter the frequency of high-ozone episodes. Rieder et al. (2013) used methods from extreme value
theory statistics to characterize changes over the eastern United States. Rieder et al. (2015) applied a statistical bias correction to 21 st century simulations with the GFDL CM3 model to project future changes. They found a simple relationship between simulated changes in 1 year return levels and regional NOx emission changes, implying that findings can be generalized to estimate changes in the frequency of eastern U.S. pollution events under different regional NO x emission scenarios. An additional application of probabilistic return levels demonstrates that continued increases in global methane abundances can offset benefits otherwise attainable by
controlling non-methane ozone precursors (Rieder et al., 2018). [EPA]
Air pollution over India
Karambelas et al. (2018) used high-resolution CMAQ simulations to demonstrate that the health burden borne by populations in rural northern India from exposure to fine particles and ozone is higher than for urban populations. A high-resolution nested configuration of GEOS-Chem was developed over India to examine the chemical composition and radiative implications of fine particle pollution episodes (Karambelas et al., 2022). We then used these model simulations as a testbed to develop machine learning approaches to derive surface particulate distributions from publicly available satellite, emission, and meteorological datasets (Zheng et al., 2023). We also used an initial condition chemistry-climate model ensemble generated with the CESM2-WACCM6 model to corroborate that concentrations of fine particles have increased over the 20th century due to emissions rather than meteorological or climate changes (Hancock et al., 2023). [Earth Institute Postdoctoral Fellowship to Alexandra Karambelas; Columbia University]