Validation of IASI Satellite Ammonia Observations at the Pixel Scale Using In Situ Vertical Profiles

Abstract

Satellite ammonia (NH3) observations provide unprecedented insights into NH3 emissions, spatiotemporal variabilities and trends, but validation with in situ measurements remains lacking. Here, total columns from the Infrared Atmospheric Sounding Interferometer (IASI) were intercompared to boundary layer NH3 profiles derived from aircraft‐ and surface‐based measurements primarily in Colorado, USA, in the summer of 2014. IASI‐NH3 version 3 near real‐time data set compared well to in situ derived columns (windows ±15 km around centroid, ±1 h around overpass time) with a correlation of 0.58, a slope of 0.78 ± 0.14 and an intercept of 2.1 × 1015±1.5 × 1015 molecules cm−2. Agreement degrades at larger spatiotemporal windows, consistent with the short atmospheric lifetime of NH3. We also examined IASI version 3R data, which relies on temperature retrievals from the ERA Reanalysis, and a third product generated using aircraft‐measured temperature profiles. The overall agreement improves slightly for both cases, and neither is biased within their combined measurement errors. Thus, spatiotemporal averaging of IASI over large windows can be used to reduce retrieval noise. Nonetheless, sampling artifacts of airborne NH3 instruments result in significant uncertainties of the in situ‐derived columns. For example, large validation differences exist between ascent and descent profiles, and the assumptions of the free tropospheric NH3 profiles used above the aircraft ceiling significantly impact the validation. Because short‐lived species like NH3 largely reside within the boundary layer with complex vertical structures, more comprehensive validation is needed across a wide range of environments. More accurate and widespread in situ NH3 data sets are therefore required for improved validations of satellite products.

UK Ammonia Emissions Estimated With Satellite Observations and GEOS‐Chem

“…However, these comparisons were for earlier versions of the IASI NH 3 product. The version used here is consistent with columns derived with aircraft observations (Guo et al., 2021), though Guo et al. (2021) caution that their comparison is limited in time (summer) and location (Colorado, USA) and sensitive to errors in column estimates from integrating aircraft measurements.…”

“…The version used here is consistent with columns derived with aircraft observations (Guo et al., 2021), though Guo et al. (2021) caution that their comparison is limited in time (summer) and location (Colorado, USA) and sensitive to errors in column estimates from integrating aircraft measurements. There are no observations of the vertical distribution of NH 3 over the UK.…”

Monthly Patterns of Ammonia Over the Contiguous United States at 2‐km Resolution

“…Accurate modeling of boundary layer height, vertical profiles of temperature, humidity, and NH 3 within the boundary layer, aerosol partitioning, and chemical lifetime are all needed to fully transform these column maps into accurate spatiotemporal emission inventories. Finally, additional validations ( Guo et al, 2021 ) of satellite-derived NH 3 columns are also needed to reduce biases at these scales (especially for conditions of temperature inversions during winter and in valleys).…”

A space view of agricultural and industrial changes during the Syrian civil war

“…The 2 instruments showed high agreement, with a Pearson's correlation coefficient R ¼ .75. A recent validation of the IASI NH 3 product using reconstructed in situ columns based on aircraft profile measurements showed very good agreement (Guo et al, 2021).…”