Regional NOx emission strength for the Indian subcontinent and the impact of emissions from India and neighboring countries on regional O3 chemistry

[ 1] This study examines the regional NOx emission strength and influence of external emissions on O-3-related chemistry over the Indian subcontinent based on a three-dimensional chemistry transport model and space-based observations, following up on our earlier work on NOx chemistry over southern Asia. NOx mass and emissions from Global Ozone Monitoring Experiment ( GOME) and Model of Atmospheric Transport and Chemistry-Max Planck Institute for Chemistry Version ( MATCH-MPIC) over India are compared, and the uncertainties in the estimates are briefly discussed. This study also employs the concept of small-perturbation tendencies to compute the scaled sensitivities with modified NOx emissions for India and the neighboring continents. The sensitivities of NOx, O-3, OH, and reservoir species of NOx over India to NOx emission from India, Southeast Asia, Africa, China, and the Middle East are discussed with respect to the photochemistry and the regional meteorology. Our study suggests that the mean regional NOx emission strength for India is close to 2.5 Tg( N)/ yr with a seasonal maximum (similar to 3 Tg( N)/ yr) during April and minimum (similar to 1.6 Tg( N)/ yr) during winter. The changes in the O3 concentrations with respect to NOx and nonmethane hydrocarbon emissions from India show that southern India is relatively more sensitive to local emission.