High-Resolution Vertical Profiles of NO2 in the Lower Troposphere During DISCOVER-AQ: Using Measured Profile Shapes to Improve OMI NO2 Retrievals and Better Understand Models

The NASA DISCOVER-AQ series of field campaigns have provided a wealth of data regarding regional air quality and how it varies on horizontal and vertical scales. As part of these campaigns a unique sonde instrument developed at KNMI (Royal Netherlands Meteorological Institute) to measure NO2 has been mounted on a tethered balloon to create a series of high vertical resolution planetary boundary layer (PBL) profiles. This instrument which is based on the chemiluminescence technique measured NO2 profiles during these recent campaign at Huron, California (Jan-Feb 2013) and will participate in the DISCOVER-AQ campaign at Smith Point, Texas (Sep 2013). The NO2-sonde data can be combined with chemiluminescence NO2 data (NCAR NOxyO3) from an aircraft which spirals above both sites. The combined profiles from the tethered balloon and aircraft yield a unique multi-city, multi-season dataset of lower tropospheric NO2 profiles. These profiles capture diurnal variations in profile structure linked to boundary layer development dynamics and will be used to evaluate errors in OMI NO2 retrievals due to a priori NO2 vertical profile shapes. Further, these profiles are compared to column amounts and profiles characteristics in the CMAQ model to shed light on processes which drive the vertical distribution of NO2 in the lower troposphere.

Over 100 high vertical-resolution PBL NO2 profiles (surface to 500m agl) and over 30 combined aircraft-sonde profiles (surface to 2500m agl) exhibit changes in the vertical distribution of NO2 consistent with an evolving boundary layer. Coherent vertical layer structures have been captured in the early- and mid-morning periods in contrast to more well-mixed profiles measured in the afternoon. An overview of the similarities and differences in profile structure between sites is presented as well as an analysis of the validity of OMI assumed profile shapes and CMAQ modeled NO2 columns and profiles. This works aims at filling a critical gap in current knowledge of NO2 vertical structure in the lower troposphere— information needed for improvement of satellite retrieval of NO2 columns as well as better understanding of the processes driving NO2 vertical distribution in air quality models.