EOS-AURA Science Team Meeting September 2009, Leiden Comparison of NO 2 profiles derived from MAX-DOAS measurements and model simulations Folkard Wittrock, Katrijn Clémer and the NO 2 profiling team

Objectives of the Bremen workshop in November To present the „state of the art“ in tropospheric profiling of NO 2 (and other trace gases) To identify advantages but also limitations of the different methods To collect ideas how to improve the methods and how to move on in the future e.g. harmonize MAXDOAS instruments and retrievals

BIRA MAXDOAS VMR surface layer compared to EMPA in situ MAXDOAS vs. in situ courtesy: Katrijn Clémer, BIRA

VMR surface layer compared to Bremen in situ MAXDOAS vs. in situ In situ BREAM GL

NO 2 Profile Comparison first comparisons sometimes o.k., sometimes not challenge is to identify what causes the differences -> model study 25 June 23 June

IASB-BIRA has provided modeled NO 2 slant columns for UV and visible, using 8 different NO 2 scenarios (profiles) 2 aerosol loadings (AOD 0.14 and 0.54 for 477 nm) aerosol information based on CIMEL data from Cabauw HG phasefunction with asymmetry factor of 0.67 Simulations for June 24, 2009 in Cabauw 10 Elevation Angles (1,2,4,5,6,8,10,15,30,89) SCD error based on real DOAS fit errors plus Gaussian noise Calculations with LIDORT Simulation study

Fixed settings for OE retrieval algorithms 0 to 4 km Apriori 1 ppb at the surface, 0.01 ppb at the top S a 100% 2 retrievals per situation and wavelength Height grid 50 and 200m -> In total 64 retrievals In total 5 groups (BIRA, MPI, NIWA, iup Bremen, WSU) have calculated data (4 OE, one „simple“ least squares method, only one result for each situation) Simulation study

Bremen retrieval of block profile for low aerosol (UV)

Simulation study Bremen retrieval of block profile for high aerosol (UV)

Simulation study Exponential low pollution, low aerosol

Simulation study Exponential high pollution, low aerosol

Simulation study Block low pollution, low aerosol

Simulation study Block high pollution, low aerosol

Simulation study Very shallow layer, low aerosol

Simulation study Less shallow layer, low aerosol

Simulation study Uplifted layer, low pollution, low aerosol

Simulation study Uplifted layer, high pollution, low aerosol

Simulation study Exponential low pollution, high aerosol

Simulation study Exponential high pollution, high aerosol

Simulation study Block low pollution, high aerosol

Simulation study Block high pollution, high aerosol

Simulation study Very shallow layer, high aerosol

Simulation study Less shallow layer, high aerosol

Simulation study Uplifted layer, low pollution, high aerosol

Simulation study Uplifted layer, high pollution, high aerosol

Simulation study

Conclusions OE retrieval methods agree quite well to each other, … but not always to „reality“ VC usually captured well also for difficult conditions Viewing directions towards sun and for high SZA difficult to retrieve Best settings for OE still open: Finer grid gives more details, but tends to more oscillations -> Elena has the solution? UV retrieval seems to be more stable Is OE the best method for MAXDOAS retrievals?

Outlook Waiting for more groups to contribute (e.g. JAMSTEC on simulated data, MPI on real data), same deadline as for aerosols -> Mid April Profiling paper: NO 2 profile intercomparison focusing on MAXDOAS capabilities and using LIDAR and in situ as complementary data sets (CWG: F. Wittrock, K. Clemer, H. Irie, S. Beirle?) Draft to be written in April 2010 before EGU

Bremen - EMPA Slope : 1.11 Correlation : Bremen – RIVM Slope : Correlation : Comparison of Bremen in situ Instrument with Empa and RIVM (at ground level) Empa sees ca. 10 % more NO2 In situ instruments BLC instruments agree quite well

In situ instruments deviation between surface in-situ and 200 m in-situ gives information on boundary layer mixing

In situ instruments NO 2 often not well mixed even in the lowest 200 m