Accounting for NOx emissions from biomass burning and urbanization doubles existing inventories over South, Southeast and East Asia

Rapid urbanization and broad use of biomass burning have led to important changes in NOx [sum of nitrogen dioxide and nitrous oxide] emissions across South, Southeast, and East Asia, frequently occurring on day-to-day time scales and over areas not identified by existing emissions databases. Here we compute NOx emissions using remotely sensed NO2 [nitrogen dioxide] and a model-free mass-conserving inverse method, resulting respectively in 61 kt d−1 and 40 kt d−1 from biomass burning in Northern and Southern Continental Southeast Asia, and 14.3 kt d−1 and 3.7 kt d−1 from urbanization in China and Eastern South Asia, a net increase more than double existing inventories. Three observationally based physical constraints consistent with theory are found which current chemical transport models cannot match: more NO2 per unit of NOx emissions, longer and more variable in-situ lifetime, and longer-range transport. This result provides quantitative support for mitigation efforts targeting specific events, processes, or geographies. Quantifying daily NOx emissions from a comprehensive range of sources indicates that half of emissions are omitted from existing inventories over South, Southeast and East Asia, suggests an analysis combining remotely sensed nitrogen dioxide and a model-free mass-conserving inverse method.