ARL Weekly News – (May 6, 2024)

Recent Events

NOAA Air Resources Car at Maryland Day

Three people standing in front of a car and a large tv displaying data

(L to R) Phillip Stratton, Jiayang Sun and Xinrong Ren with the Air Resources Car at UMD.

ARL brought the Air Resources Car (ARC) out to the annual Maryland Day event at the University of Maryland campus in College Park, MD on Saturday, April 27, 2024. Despite the rainy weather, tens of thousands of people came out to the college campus. Scientists Xinrong Ren, Phillip Stratton and Jiayang Sun and ARL Director Ariel Stein interacted with many of them as they stopped by the ARC telling them about the instruments, measurements and the overall mission. Members of the public were also delighted to be able to test some of the sensors for themselves by blowing into a tube and seeing the ambient amount of carbon dioxide detected rise dramatically on the data streaming live on a large monitor.






Air Resources Car at NOAA’s 2024 North Atlantic Regional Team Annual Meeting

Three people standing around a black SUV with the NOAA logo on the side. Various instruments are mounted to the roof.

Jiayang Sun talks about the ARC to some of the meeting attendees.

On May 1, Phil Stratton, Jiayang Sun, and Xinrong Ren were invited to participate in NOAA’s 2024 North Atlantic Regional Team Annual Meeting in Baltimore. The primary goal of the meeting was to engage with local partners and experts in NOAA’s mission to advance equity, promote the blue economy, and foster a climate-ready nation.

During the meeting, Phil, Jiayang, and Xinrong presented the Air Resources Car (ARC) and its related research to the meeting attendees. They explained the innovative features of the ARC and its significance in monitoring air quality and greenhouse gases.

The presentation underscored the importance of real-time data collection and analysis in addressing air quality challenges, particularly in the context of climate change and environmental justice. During the presentation, potential opportunities for collaboration were also discussed. The presentation of the ARC was well received, generating positive feedback and interest among attendees.




GRAAPES Annual Meeting

Chris Loughner participated in the GReenhouse gas And Air Pollutants Emissions System (GRAAPES) annual meeting on May 6, in Washington, DC. The GRAAPES project is a joint NOAA – NIST initiative to model and map greenhouse gas and air pollutant emissions and their uncertainties across CONUS. Chris Loughner gave a brief presentation discussing the Urban Greenhouse Gas Emissions Measurements and Monitoring System (Urban-GEMMS) project, which involves developing a semi-operational top-down greenhouse gas emissions estimation system for the Washington, DC – Baltimore, MD metropolitan area based on measurements of greenhouse gases within the urban corridor. The GRAAPES emissions inventory is being used within the Urban-GEMMS project as an initial first guess of emissions estimates in the Washington, DC – Baltimore, MD metropolitan area. Improved emissions estimates from the Urban-GEMMS system will be passed back to the GRAAPES team to aid in improving the GRAAPES emissions inventory.


Weather balloon launch supporting the NWS

On the afternoon of 8 May, Temple Lee, Dominick Christensen, Kurt Daniels, Tom Wood, and Randy White performed a weather balloon launch from ATDD to support forecasting operations at the the NWS Weather Forecast Office in Morristown. The measurements obtained provided important information about low-mid level wind shear, boundary layer destabilization, and airmass recovery following that morning’s convection and prior to a severe squall line that impacted the area later that evening.


Published:  Improving the atmospheric dispersion forecasts over Washington, D.C. using UrbanNet observations: A study with HYSPLIT model

Nebila Lichiheb, Font Ngan, and Mark Cohen, 2024: Improving the atmospheric dispersion forecasts over Washington, D.C. using UrbanNet observations: A study with HYSPLIT model. Urban Climate,


UrbanNet data have been used to enhance the predictions of the Weather Research and Forecasting (WRF) model through observational nudging to improve temperature and wind predictions. HYSPLIT was utilized to understand the impact of using the observationally nudged WRF fields in dispersion modeling. The meteorological observations collected from the National Weather Service monitoring stations located at two major airports in the Washington metropolitan area were also assimilated into WRF modeling. The results showed that observational nudging successfully adjusted WRF wind fields towards the observations and significantly reduced the forecast temperature bias at nighttime. The comparison of HYSPLIT simulations with and without the enhancement of the WRF model using UrbanNet and airport data showed significant differences in the pattern and direction of the dispersion plume especially during the early morning hours. Furthermore, ingesting the data from the closer airport to the downtown area in WRF provided HYSPLIT simulations very similar to the ones using UrbanNet data. This provides strong evidence that local data are essential to adjust weather prediction models routinely used to drive dispersion models. There was also evidence of increased mixing height when using local data collected in the downtown, mainly resulting from the increased surface heating in the city.


Published: Evaluation of soil water content and bulk electrical conductivity across the U.S. Climate Reference Network using two electromagnetic sensors

Timother B. Wilson, John Kochendorfer, Howard J. Diamond, Tilden P. Meyers, Mark Hall, Temple R. Lee, Rick D. Saylor, Praveena Krishnan, Ronald D. Leeper and Michael A. Palecki, 2024: Evaluation of soil water content and bulk electrical conductivity across the U.S. Climate Reference Network using two electromagnetic sensors. Vadose Zone Journal,


Soil bulk electrical conductivity (BEC) was evaluated alongside soil volumetric water content (VWC) and soil temperature measurements using the HydraProbe (model HydraProbe, Stevens Water Monitoring Systems, Inc.) (hereafter called HP) with accuracy range of BEC ≤ 0.3 S m−1, and the time domain reflectometry (TDR)-315L Probe (model TDR-315L, Acclima, Inc.) (hereafter called AP) suitable for BEC up to 0.6 S m−1, at 23 stations of the U.S. Climate Reference Network. Previous evaluations revealed inconsistent performance of both sensors in some clay soils using manufacturer-recommended calibrations in converting dielectric permittivity measurements to VWC. Here, we found that hourly values of BEC reached 0.6 S m−1 in high clay content soils and exceeded 2 S m−1 in high saline soils, and these high values of BEC were associated with poor performance and failures of both HP and AP sensors. Large values of BEC occurred in predominantly saturated soils where VWC values reached about 0.5 m3 m−3 for saline soils and about 0.7 m3 m−3 for clay soils, while low magnitudes of BEC were associated with low soil water content and seldomly saturated soils. Low hourly BEC values of less than 0.1 S m−1 were observed in wide variety of soil types, where sensor performance was typically excellent. The most influential factor on BEC was high soil water content conditions. Although dielectric permittivity measurements in estimating the soil water content were sensitive to BEC as some high clay content and high salinity soils increased BEC, the impact of large BEC on dielectric permittivity measurements was smaller in the well-drained top soil layers than in deep soil layers that remained near saturation. Soil temperature had only a small impact on BEC. With high clay content and high salinity, the specific area of clay minerals was also associated with the magnitude of BEC.