Evaluation of the Potential of Sentinel-5P TROPOMI and AIS Marine Traffic Data for the Monitoring of Anthropogenic Activity and Maritime Transport NOx-Emissions in Canary Islands Waters

Abstract

This work studies air quality by analysing NOx emissions in the inland waters of the Canary Islands, with particular emphasis on determining how maritime transport activity contributes to the emission of NO2 in the environment of the two main islands, Tenerife and Gran Canaria. We explored the capabilities of tropospheric NO2 density derived from the TROPOMI sensor onboard ESA’s Sentinel 5P Satellite to be used as an air quality monitoring tool at the regional scale of the Canary Islands. The studied mesoscale emission scenarios allowed us to identify the main sources, associated with urban areas, heavy roads, power plants, ports, and to a lesser extent, shipping routes. Mean values for the metropolitan area of Santa Cruz de Tenerife were 1.38 × 1015 molec cm−2. Similarly, in port areas, mean values of 1.22 × 1015 molec cm−2 were found. These levels can confidently be associated with anthropogenic activities. These were clearly distinguishable from background (noise) values of 7.08 × 1014 molec cm−2 obtained in maritime areas away from the influence of the islands. To investigate the maritime contribution to the NO2 emissions, ship tracks were obtained from an Automated Identification System (AIS) receiving station that covered the channel between the Tenerife and Gran Canaria islands. Multitemporal, and hence accumulative, NO2 scenarios were compared with the ship traffic density within a given temporal window before satellite overpass. We found good spatial agreement between NO2 signal and frequent ship routes between the major islands at several time scales, particularly in weekly averaged scenarios. Enhancements up to 2.0 × 1015 molecules cm−2 relative to surrounding waters were identified in the middle of the main shipping routes between the main islands. Thus, multitemporal NO2 scenarios derived from TROPOMI can lead to an estimate of the ship traffic contribution to NOx emissions in complex environments, such as this one, influenced by land emissions.