Tracking down global NH<sub>3</sub> point sources with wind-adjusted superresolution

Abstract

As a precursor of atmospheric aerosols, ammonia (NH 3 ) is one of the primary gaseous air pollutants. Given its short atmospheric lifetime, ambient NH 3 concentrations are dominated by local sources. In a recent study, Van Damme et al. (2018) have highlighted the importance of NH 3 point sources, especially those associated with feedlots and industrial ammonia production. Their emissions were shown to be largely underestimated in bottom-up emission inventories. The discovery was made possible thanks to the use of oversampling techniques applied to 9 years of global daily IASI NH 3 satellite measurements. Oversampling allows one to increase the spatial resolution of averaged satellite data beyond what the satellites natively offer. Here we apply for the first time superresolution techniques, which are commonplace in many fields that rely on imaging, to measurements of an atmospheric sounder, whose images consist of just single pixels. We demonstrate the principle on synthetic data and on IASI measurements of a surface parameter. Superresolution is a priori less suitable to be applied on measurements of variable atmospheric constituents, in particular those affected by transport. However, by first applying the wind-rotation technique, which was introduced in the study of other primary pollutants, superresolution becomes highly effective in mapping NH 3 at a very high spatial resolution. We show that plume transport can be revealed in greater detail than what was previously thought to be possible. Next, using this windadjusted superresolution technique, we introduce a new type of NH 3 map that allows tracking down point sources more easily than the regular oversampled average. On a subset of known emitters, the source could be located within a median distance of 1.5 km. We subsequently present a new global point-source catalog consisting of more than 500 localized and categorized point sources. Compared to our previous catalog, the number of identified sources more than doubled. In addition, we refined the classification of industries into five categories -fertilizer, coking, soda ash, geothermal and explosives industries -and introduced a new urban category for isolated NH 3 hotspots over cities. The latter mainly consists of African megacities, as clear isolation of such urban hotspots is almost never possible elsewhere due to the presence of a diffuse background with higher concentrations. The techniques presented in this paper can most likely be exploited in the study of point sources of other short-lived atmospheric pollutants such as SO 2 and NO 2 .

High-resolution hybrid inversion of IASI ammonia columns to constrain US ammonia emissions using the CMAQ adjoint model

“…where E t and E a are the new and a priori emission estimates, respectively. The method has been described in detail in previous studies (Li et al, 2019;Cooper et al, 2017;Martin et al, 2003). The IMB is applied at the coarse grid so that the NH 3 column will be dominated by the local emissions instead of transport from neighboring grids (Li et al, 2019).…”

Multiscale observations of NH3 around Toronto, Canada

“…A study by Hu et al (2014) investigating NH 3 in downtown Toronto has shown that greenery within the city is an important source of NH 3 when temperatures are above freezing, and that potential sources at temperatures below freezing have yet to be investigated. Additionally, recent studies have shown the increased capacity for satellite-based instruments to measure spatial and temporal distributions of NH 3 total columns at global Warner et al, 2016;Shephard et al, 2020), regional Warner et al, 2017;Viatte et al, 2020), and point-source scales (Van Damme et al, 2018;Clarisse et al, 2019a;Dammers et al, 2019).…”

Record high levels of atmospheric ammonia over India: Spatial and temporal analyses

“…A detailed inventory of NH 3 hotspots using a decade of IASI NH 3 measurements is provided in Van Damme et al (2018). Clarisse et al (2019aClarisse et al ( , 2019b have presented a wind-adjusted superresolution technique to allow a better identification of weak point sources of atmospheric NH 3 . We have considered the reanalyzed NH 3 total column data (ANNI-NH3-v2.2R-I) (Whitburn et al, 2016a(Whitburn et al, , 2016bVan Damme et al, 2017).…”

“…Here, we use the IASI satellite measurements to analyse the seasonal and inter-annual variability of atmospheric NH 3 over India for the period 2008-2016. These measurements have been used in the past to delineate global industrial, agricultural, and natural NH 3 hotspots (Van Damme et al, 2018;Clarisse et al, 2019aClarisse et al, , 2019b. Detailed interseasonal and inter-annual analyses of atmospheric NH 3 over India, however, have not been performed yet (Clarisse et al, 2009;Tanvir et al, 2019).…”