Air Quality Projects

AER scientists perform cutting-edge research on atmospheric chemistry, pollutant dispersion, and the dependence of both on meteorology for a variety of agencies (e.g. NSF, NASA, NOAA). AER’s Air Quality team uses the scientific and technical expertise gained in these efforts to support federal, regional, state, local, and tribal air quality agencies, as well as non-profit and industry clients, in addressing their air quality challenges. We work with our clients to design air quality modeling and data analysis studies that meet our clients’ scientific, technical, and regulatory needs while staying within the required schedule and budget.

Selected AER Air Quality Projects

Projects Details

Meteorological Modeling for TCEQ Air Quality Studies
AER developed and validated an improved configuration of the WRF model to provide the Texas Commission on Environmental Quality (TCEQ) with high spatial- and temporal-resolution meteorological fields for the NASA DISCOVER-AQ Houston campaign and for recent high O3 events in El Paso. The model configurations had an inner grid with a 1.33 km horizontal resolution to provide better representation of the meteorology leading to O3 exceedances in Houston and El Paso. AER incorporated a 1 km resolution sea surface temperature analysis into WRF to better represent the Galveston Bay Breeze and used an Urban Canopy Model to account for the interaction between the urban landscape of Houston and the atmosphere.

Investigating the Controls of Urban O3 and PM2.5 for TCEQ
AER researched the controls of O3 and PM2.5 in seven urban areas in Texas for the Texas Commission on Environmental Quality (TCEQ). For each urban area, AER analyzed air quality data provided by TCEQ to:

  • Determine the effects of meteorology on trends in O3 and PM2.5 by fitting a generalized additive model for O3 and PM2.5 concentrations to selected meteorological variables.
  • Estimate the regional background concentrations of O3 and PM2.5.
  • Investigate the synoptic and urban-scale conditions that are associated with high concentrations of O3 and PM2.5.
  • Develop models to forecast tomorrow’s O3 concentration based on the most recent weather forecast.

An Exceptional Event Screening Tool to Identify Stratospheric Impacts on Ozone Exceedances
The EPA has put forth an Exceptional Events Rule that provides a mechanism by which air quality data can be excluded from regulatory decisions if an exceptional event causes an exceedance of the NAAQS ozone standard. These exceptional events can be caused by natural phenomena such as wildfires and stratospheric intrusions. The current EPA guidance for an exceptional event demonstration requires detailed modeling and analysis work to be done for each event, but states, such as Texas, have limited resources to perform extensive investigations of every ozone exceedance.

To help with this problem, AER developed an exceptional events screening tool that efficiently determines which ozone exceedance days were significantly impacted by stratospheric ozone intrusions upwind of the reporting monitor. This allows states to identify which events should be further investigated with a full photochemical model study. The tool includes a back-trajectory component, based on the Stochastic Time Inverted Lagrangian Transport (STILT) model, that determines the multiple source regions of air transported to the reporting monitor. A second component uses satellite observations of ozone to estimate the impact of a stratospheric intrusion at the monitor. The tool provides a metric that indicates the likelihood that an exceptional event has occurred, thus allowing air quality managers to allocate modeling resources more efficiently and ultimately help in determining the contribution of natural sources to local ozone pollution.

CMAQ Model Evaluation with Surface, Aircraft, and Satellite Data
AER led two research projects funded by the NOAA Climate Program Office to investigate the emissions and impacts of the aerosol precursors NH3, NOx, and SO2. These projects used data from NOAA field campaigns, satellite retrievals of NH3, NO2, and SO2, and the Community Multi-scale Air Quality (CMAQ) model to improve estimates of the emissions of these gases. Our results for California, published in the journal Atmospheric Chemistry and Physics, showed that correctly specifying the diurnal cycle and bi-directional flux of agricultural NH3 emissions is critical to the modeling of atmospheric NH3. Furthermore, we have demonstrated that NH3 observations from the Cross-Track Infrared Sounder (CrIS) can be used to derive monthly-mean scaling factors that significantly improve upon a priori NH3 emissions at typical resolutions for air quality modeling. This work is being extended in a NASA Applied Science project to provide improved emission inventories of NH3 to air quality managers, forecasters, and other stakeholders.

Identifying and Quantifying Natural Gas Leaks in Boston for the EDF
AER participated in a Harvard-led study of the contribution of natural gas leaks to emissions of methane in the Boston area. The study, partially funded by the non-profit Environmental Defense Fund (EDF) and published in the prestigious journal Proceedings of the National Academy of Sciences, found that about 2.7% of all natural gas delivered to the region was being lost to leaks from homes, businesses, and electricity generation facilities, substantially more than estimated by government authorities (1.1%).

The WRF-STILT model used in this project was developed at AER and is the linchpin of multiple GHG-related efforts worldwide. On-going applications of WRF-STILT include studies of methane emissions over the Arctic and of carbon dioxide emissions over the Northeast corridor of the US.

Determining Impacts of Soot on Himalayan Glaciers for the World Bank
Snowmelt, icemelt, and rain from the Himalaya, Karakoram, and Hindu Kush mountain ranges forms the source of the Indus, Ganges, and Brahmaputra rivers which are the major source of fresh water for 750 million people. Soot (also called black carbon) transported to the mountains from polluted areas is increasing the absorption of solar radiation by the glaciers, which is leading to loss of the glaciers and the freshwater source they provide.

In order to better understand the impacts of climate change and soot emissions on the South Asian glaciers and the potential impacts on the freshwater sources, AER worked with the World Bank and collaborators from Duke University, NASA, and NCAR to use the combined weather and atmospheric chemistry model WRF-Chem to determine the sources contributing to the soot on the glaciers both under current conditions and in 2050 using projections of future controls to reduce soot emissions. The results of this study were published in the Journal of Geophysical Research-Atmospheres. We found that brick kilns and wood burning stoves in South Asia are a significant source of soot, but that sources outside of South Asia contribute an equal amount to the soot on the glaciers. This information will be used by the World Bank and the nations of South Asia to inform soot control policies and freshwater management policies that will help to protect human health and economic development in South Asia as the global climate continues to change.

Forecasting Dust Storms for the Air Force
AER substantially improved the ability of the Air Force to forecast dust storms using the WRF-Chem model. After determining that the original dust emission parameterization included in WRF-Chem resulted in a large number of false predictions of dust storms, AER designed and implemented a new dust emission parameterization with updated physics into WRF-Chem along with a high-resolution map of dust source regions, approaches for improved soil moisture handling, and a dynamic vegetation mask. AER then validated this updated dust storm forecast system using dust hazard reports, surface visibility observations, and aerosol optical depth (AOD) observations from surface and satellite instruments. The updated forecast substantially decreased the number of false dust storm predictions and improved overall forecast skill by 30%, and the new dust parameterization is now the recommended dust emission parameterization for WRF-Chem.

Advancing the Use of Satellite Observations to Study Air Quality
AER is a leader in the development, validation, and use of satellite retrievals for air quality and atmospheric chemistry studies. AER has worked on the development of trace gas retrievals from NASA’s Tropospheric Emission Spectrometer (TES) for species such as methane, ammonia, formic acid, and methanol. In 2014, AER led the Cross-track Infrared Spectrometer (CrIS) Atmospheric Chemistry Data User’s Workshop to develop a strategic plan to use CrIS observations in air quality and atmospheric composition research. AER also led the development of ammonia retrievals from CrIS and pioneered their application to air quality studies, developing an inversion framework to provide better estimates of ammonia emissions in North America. For the World Bank, AER evaluated the ability of satellites to improve the monitoring of fine particulate matter (PM2.5) in low- and middle-income countries and made recommendations for the use of satellite data in these countries.

Expert Evaluation of Meteorological Inputs for Air Quality Modeling for SESARM
AER led a detailed analysis of the WRF meteorological fields provided by the Southeastern States Air Resource Managers, Inc. (SESARM) to determine if the data were suitable for subsequent use in air quality modeling. Ten WRF model configurations were evaluated using a combination of objective analysis (WRF-MET software to compare the model data to meteorological observations) and expert judgment. AER then designed a simple-to-use website that gave access to all of the objective evaluation results in graphical and text formats. This permitted rapid dissemination of hundreds of thousands of validation results to SESARM and its members.