Princeton On-road Ammonia

On-road Ammonia Emissions:

Ammonia (NH3) is a key precursor to atmospheric fine particulate matter, with strong implications for regional air quality and global climate change. On-road NH3 emissions by vehicles take a significant fraction of total NH3 sources.

A mobile platform is developed by mounting our open-path NH3 sensor  with other open-path trace gas sensors on top of a passenger car. We have performed on-road measurements in the US and China, covering over 10,000 km. We demonstrate that mobile, open-path measurements provide a more comprehensive quantitative understanding of on-road NH3 emissions in urban and suburban settings.

Reference: Sun et al., ES&T

Animation: [Ammonia in Beijing, China] [Ammonia in Houston, TX]

Open-path ammonia eddy covariance flux

Open-path Ammonia Eddy Covariance Flux:

The strong surface affinity of NH3 makes it challenging to measure, especially at low concentration and high sampling frequency. Closed-path measurements of NH3 are complicated by large and uncertain response time, unknown buffering of large changes in concentration, and ambiguity between NH3 and ammonium due to phase transitions in sampling lines.

Only recently, several sensitive and fast responding instruments for NH3 became available. Our first test showed promising results, demonstrating the advantages of open-path NH3 sensors in eddy covariance flux measurements.

Reference: Sun et al., AFM; Sun et al., BLM

TES intercomparison

Validation of Satellite Ammonia Retrieval :

Satellite observations, including TES/Aura, IASI/MetOp, and CrIS/NPP, provide unique datasets to quantify ammonia emissions and distributions from global to regional scales. The wide ranges of conditions in which TES measures reinforce the importance of extensive validation with in-situ measurement in different areas.

Coordinated with the TES team, we drove directly under TES transect on January 21, 28, and 30. Initial intercomparison shows good correlation between our ground-based mobile measurements and TES RVMR.

Reference: Sun et al., JGR-A

Mobile sensors in CAREBeijing

Development of High Sensitity/Mobility Open-path Sensor Systems:

We have developed a mobile platform that measures multiple important trace gases (including CO2, CO, CH4, H2O, N2O and NH3) with both custom-made and commercial open-path portable gas sensors. We endeavored to make the measurements reliable, repeatable, and stable on the car top. Our mobile platform can be readily installed in passenger vehicles. This multi-gas mobile platform shows very promising performance and gives new insights for local scale urban and agricultural emissions in field campaigns.

References: Miller et al., AMT; Tao et al., OE

Inline calibration

Continous, In-situ Calibration of Open-path Sensors by an Inline Reference Cell:

Ethylene (C2H4) has an absorption feature partially offset from the ammonia absorption feature, and the ethylene signal serves as a reference signal for ammonia concentration in real time. Multiple harmonic wavelength modulation spectroscopy (WMS) signals are used to separate the ambient ammonia and reference ethylene absorption signals. The ammonia signal is detected with the second harmonic (2f), while it is calibrated simultaneously with a high-harmonic (6-12f) signal of ethylene.

Similar technologies have been applied in open-path N2O and CH4 detections.

Reference: Sun et al., APB; Miller et al., AMT; Tao et al., OL