No abstract

[1] This study examines the regional NO x emission strength and influence of external emissions on O 3 -related chemistry over the Indian subcontinent based on a threedimensional chemistry transport model and space-based observations, following up on our earlier work on NO x chemistry over southern Asia. NO x 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 NO x emissions for India and the neighboring continents. The sensitivities of NO x , O 3 , OH, and reservoir species of NO x over India to NO x 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 NO x emission strength for India is close to 2.5 Tg(N)/yr with a seasonal maximum ($3 Tg(N)/yr) during April and minimum ($1.6 Tg(N)/yr) during winter. The changes in the O 3 concentrations with respect to NO x and nonmethane hydrocarbon emissions from India show that southern India is relatively more sensitive to local emission.

The sensitivity of the Indian Ocean atmospheric chemistry to continental NOx emissions is examined using a global chemistry‐transport model (MATCH‐MPIC). NOx responds nonlinearly to changes in emissions, since O3 and OH, which depend on NOx, influence its lifetime. Due to this feedback and the contribution from other NOx sources (e.g., lightning), much of the Indian Ocean lower troposphere (LT) is only weakly sensitive to continental NOx emissions. In contrast to INDOEX (Indian Ocean Experiment) results for aerosols, CO, etc., during the winter monsoon the central Indian Ocean (CIO) is weakly sensitivity to Indian NOx emissions. However, the Bay of Bengal LT is very sensitive to NOx emissions from India (summer) and SE Asia and China (winter). Higher up, NOx over the CIO is most sensitive to African and SE Asian emissions, while the northern regions are influenced by the summer monsoon plume from India, SE Asia and China.

[1] In this study we identify recurring plumes of tropospheric NO 2 originating from Africa and Indonesia during the monsoon transition periods over the central Indian Ocean (CIO, 5°N-30°S, 55°E-95°E), based on GOME satellite observations and global model (MATCH-MPIC) simulations. Despite the relatively short lifetime of NO x , these strong plumes can develop due to the pronounced anti-cyclonic circulation over the CIO, and the weak maritime convection, which limits vertical mixing. Model results indicate that the plumes are mainly transported in the middle troposphere (MT). Thus, the CIO in the Southern Hemisphere (SH) is not always as pristine as found in INDOEX during the winter monsoon.