Validation of TES ammonia observations at the single pixel scale in the San Joaquin Valley during DISCOVER‐AQ

Abstract

Ammonia measurements from a vehicle-based, mobile open-path sensor and those from aircraft were compared with Tropospheric Emission Spectrometer (TES) NH 3 columns at the pixel scale during the NASA Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality field experiment. Spatial and temporal mismatches were reduced by having the mobile laboratory sample in the same areas as the TES footprints. To examine how large heterogeneities in the NH 3 surface mixing ratios may affect validation, a detailed spatial survey was performed within a single TES footprint around the overpass time. The TES total NH 3 column above a single footprint showed excellent agreement with the in situ total column constructed from surface measurements with a difference of 2% (within the combined measurement uncertainties). The comparison was then extended to a TES transect of nine footprints where aircraft data (5-80 ppbv) were available in a narrow spatiotemporal window (<10 km, <1 h). The TES total NH 3 columns above the nine footprints agreed to within 6% of the in situ total columns derived from the aircraft-based measurements. Finally, to examine how TES captures surface spatial gradients at the interpixel scale, ground-based, mobile measurements were performed directly underneath a TES transect, covering nine footprints within ±1.5 h of the overpass. The TES total columns were strongly correlated (R 2 = 0.82) with the median NH 3 mixing ratios measured at the surface. These results provide the first in situ validation of the TES total NH 3 column product, and the methodology is applicable to other satellite observations of short-lived species at the pixel scale.

Ammonia and methane dairy emission plumes in the San Joaquin Valley of California from individual feedlot to regional scales

“…Finally, the NH 3 :CH 4 ER was consistently larger in the midafternoon transect relative to the morning or midday, but this difference is within the measurement uncertainty when comparing the midday and afternoon transects (Figure b). This trend is potentially linked to higher NH 3 surface emissions in the midafternoon due to increased solar heating and surface temperatures relative to CH 4 emissions and consistent with other studies of diurnal NH 3 and CH 4 flux measurements [ van Haarlem et al , ; Sun et al , ]. Further investigation is needed to attribute these mechanisms to the observed trends.…”

Evaluating ammonia (NH3) predictions in the NOAA National Air Quality Forecast Capability (NAQFC) using in situ aircraft, ground-level, and satellite measurements from the DISCOVER-AQ Colorado campaign

“…The 1-min averages were used for model-tomeasurement comparisons. The PTR-MS measurement system for NH 3 was evaluated in a previous DISCOVER-AQ campaign in the San Joaquin Valley of California (Sun et al, 2015). The PTR-MS system was found to have a measurement accuracy of ±35% and a 1s measurement precision of 5.5e6.5 ppbv at 1 s time resolution, or 0.75 ppbv for a 1-min average.…”

“…P3B aircraft measurements of NH 3 and NH 4 þ are described in detail in Sun et al (2015). Ambient air was directed to an array of instruments located on-board the aircraft.…”

Validation of the CrIS fast physical NH&lt;sub&gt;3&lt;/sub&gt; retrieval with ground-based FTIR

“…However, the overall quality of the satellite observations is still highly uncertain due to a lack of validation. The few validation studies showed a limited vertical, spatial and or temporal coverage of surface observations for a proper uncertainty analysis (Van Damme et al, 2015b;Sun et al, 2015). A recent study by Dammers et al (2016a) explored the use of Fourier transform infrared (FTIR-NH 3 , Dammers et al, 2015) observations to evaluate the uncertainty of the IASI-NH 3 total column product.…”