Trace Gas Atmospheric Rivers: Remote Drivers of Air Pollutants

Over the decade, numerous NASA satellites are providing essential information about the state of the Earth’s environ- ment and air quality. To assess the effects of climate and environmental change on atmospheric composition, it is essential to develop a comprehensive analysis tool and apply it to various NASA’s satellite data. This will support environmental policy decisions to improve both air quality and climate.

Here, we present a new concept and analysis tool, trace gas atmospheric rivers (TGARs), to detect major long-range transport events of atmospheric trace gases, by extending the concept of water vapor atmospheric rivers (ARs). ARs are known to be important for transporting water vapor and can also be important for facilitating long-range transport of atmospheric pollution. This study, under NASA’s atmospheric composition modeling and analysis program (ACMAP), applies the TGAR concept to the outputs of the six-hourly global trace gas data from the NASA JPL multi-model multi- constituent chemical (MOMO-Chem) data assimilation system. MOMO-Chem ingests various satellite data to produce the complete global picture of atmospheric composition, and the output data have been evaluated against independent in-situ surface observations and satellite retrievals from TES, AIRS/OMI, and Cross Track Infrared Sounder (CrIS) de- veloped by NASA JPL TROPESS.

We analyzed the climatological seasonal patterns and inter-annual variability of integrated gas transport (IGT) of three trace gases: carbon monoxide (CO), ozone (O3), and peroxyacetyl nitrate (PAN) obtained from MOMO-Chem for 2005- 2019 (and onward). The fractional ARs contribution to total transport is also examined. Over the period, the maximum annual total transport was found over the Pacific, Atlantic, and south temperate zone. Over these regions, TGARs tend to occur 15-20 events days yr−1 which is responsible for up to >60 % of the total transport. The CO shows a declining inter-annual trend shows in most of the regions, with East China experiencing a significant change. The concentration of O3 exhibits an upward trend over North Africa, Central Asia, and the Atlantic Ocean. PAN has increased in Asia, whereas a significant change in Africa, North America, and South America could be related to wildfire events. Our study revealed that the regional IGT trends (increasing or decreasing) are similar for all trace gas species, given the common wind patterns. The decreasing IGT trend was observed over Northwest Pacific, Northeast Atlantic, and North Pacific. In contrast, the increasing trend of IGT is found over North Atlantic, Northeast Pacific, and Antarctic circumpolar regions. These contrasting trends are influenced by regional dependence of emission control, secondary processes, and extreme events transport. Meanwhile, the strength and inter-annual variability of the IGT trends differed among the three species, reflecting the different emission trends for each species, including their precursors.

The developed TGARs analysis framework will be used to provide insight into the driving mechanisms of the global distribution and variability of pollution as well as short-term extreme pollution transport events. We also expect that this framework will be useful for better understanding air quality drivers and improving chemical transport models. Future studies will consider the relative roles of various meteorological processes, such as jet stream, Rossby wave, and El Niño-Southern Oscillation (ENSO) events, as well as emission and chemical conversion processes.