Tropopause-Level NO_x in the Asian Summer Monsoon

Area of Science:

• Atmospheric Chemistry
• Monsoon Dynamics
• Satellite Remote Sensing

Background:

• Deep convection in the Asian summer monsoon (ASM) significantly impacts the upper troposphere-lower stratosphere (UTLS).
• Understanding the distribution of nitrogen oxides (NOx) in this region is crucial for atmospheric chemistry.
• The UTLS ASM anticyclone is a key region for chemical transport.

Purpose of the Study:

• To investigate the distribution of nitrogen dioxide (NO2), nitric oxide (NO), and nitrogen oxides (NOx) in the UTLS ASM anticyclone.
• To analyze satellite measurements and photochemical box model simulations of NOx species.
• To understand the factors influencing NOx concentrations within the ASM anticyclone.

Main Methods:

• Utilized satellite observations of NO2 from OMI, ACE-FTS, and SAGE III ISS.
• Employed the PRATMO photochemical box model for NOx photochemistry analysis.
• Derived NOx concentrations using OSIRIS NO2 and O3 observations.

Main Results:

• Satellite data indicated a relative minimum in NO2 over the ASM during summer months.
• Elevated NO and NOx anomalies were observed within the ASM.
• These anomalies are attributed to low ozone (O3) concentrations and cold temperatures.

Conclusions:

• The study provides insights into NOx distribution within the UTLS ASM anticyclone.
• Satellite observations show good agreement with Whole Atmosphere Community Climate Model simulations.
• Low ozone and cold temperatures are key factors controlling NOx in the region.