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

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.

Upper-tropospheric CO and O<sub>3</sub> budget during the Asian summer monsoon

“…Concerning the impact of NO x local sources on the upper-tropospheric (500-150 hPa) O 3 , Kunhikrishnan et al (2004) found a maximum of 15 %. Similar results are found by Kunhikrishnan et al (2006) with a 10 to 20 % sensitivity of O 3 to Indian NO x emissions in the middle and upper troposphere (700-200 hPa) over India. From Fig.…”

“…7g and j. We have therefore an approximate 15 % sensitivity of O 3 to the Indian NO x source in good agreement with Kunhikrishnan et al (2004Kunhikrishnan et al ( , 2006. According to Kunhikrishnan et al (2006), NO x emissions from Indonesia have a non-negligible effect on upper-tropospheric NO x (20-30 %) and O 3 (10-15 %) over India during the ASM period.…”

“…It is also interesting to note that STE also impact the free troposphere over the Middle East and India in a very similar way to African LiNO x , traveling with the westerly winds below the AMA. The same eastward transport of Middle East NO x emissions has been shown to slightly (∼ 10 %) impact NO x and O 3 distributions in the lower troposphere over India (Kunhikrishnan et al, 2006). Nevertheless, as discussed in Sect.…”

“…Sauvage et al (2007b) have shown that tropospheric O 3 over Asia during the monsoon is mostly impacted by Asian sources. Focusing on the Indian region, Kunhikrishnan et al (2006) have also highlighted the predominance of Asian sources (India, China and Indonesia) on the Indian tropospheric O 3 budget during the monsoon. They have also shown that Middle East emissions have a small impact on NO x and O 3 concentrations below 500 hPa and that African and Middle East sources have a negligible impact in the middle and upper troposphere over India during the Table 3 for O 3 and NO x average mixing ratios.…”

“…Previous studies (Kunhikrishnan et al, 2004(Kunhikrishnan et al, , 2006 have therefore dealt with the O 3 budget in the Indian troposphere, but the O 3 budget of the AMA has not yet been addressed in detail. In particular, it is not yet known to what extent the different NO x sources are responsible for an increase in the O 3 concentrations within this upper-level large-scale circulation characterized by rather low O 3 concentrations.…”