Quantifying the Missing Half of Daily NOx Emissions over South, Southeast and East Asia

Abstract Rapid urbanization and broad use of biomass burning have led to significant changes in NOx emissions across South, Southeast, and East Asia, frequently occurring on day-to-day time scales and over areas not identified by existing emissions databases. This work computes NOx emissions using remotely sensed NO2 and a model-free mass-conserving inverse method, resulting respectively in 61kt/day and 40kt/day from biomass burning in Northern and Southern Continental Southeast Asia, and 14.3kt/day and 3.7kt/day from urbanization in China and Eastern South Asia. This is a net increase of more than double the 55.7kt/day existing inventories. This method offers three additional constraints: NO2 accounts for 22%-90% of NOx emissions, NOx has an in-situ lifetime of 4.3hours-24hours, and NOx transports up to 480km, all of which are larger than chemical transport modeling studies, yet still consistent with theory. This result provides quantitative support for mitigation efforts targeting specific extreme events, processes, or geographies.