1. High vertical resolution NO 2 -sonde data: Air quality monitoring and interpretation of satellite-based NO 2 measurements D. C. Stein Zweers, A.Piters, M. Allaart, K. F. Boersma, M. den Hoede, W. Sluis, P. F. Levelt - (stein@knmi.nl) 5. Future DISCOVER-AQ Campaigns: 4. DISCOVER-AQ Results NO 2 -Sonde: 4a. Aircraft, Baltimore/Washington July 2011 6. Acknowledgements: University of Maryland aircraft CRDS data from Russ Dickerson; Millersville University tethersonde photo courtesy of Dr. Richard Clark; 1. DISCOVER-AQ: Deriving Information on Surface Conditions from COlumn and VERtically Resolved Observations Relevant to Air Quality 3. NO 2 -Sonde Overview: 2. Opportunity for OMI NO 2 Validation: Introduction and Overview: Section 1: Summary of how the NASA DISCOVER-AQ measurement campaigns can help meet OMI validation needs especially for NO2; Section 2: How the NO2-sonde can be used for OMI validation – a two-step process comparing OMI NO2 column data with vertically resolved model profiles and/or in-situ data like MAXDOAS and in turn compare with detailed NO2-sonde vertical profile structure; Section 3: Overview of how KNMI-developed NO2-sondes can fill critical data gaps about the vertical distribution of NO2; Section 4: Results from the flexible multi-platform deployment from Baltimore/Washington DC July 2011 DISCOVER-AQ campaign on an aircraft and a tethersonde balloon; Section 5: Setup for Future DISCOVER-AQ campaigns with the NO2-sonde in Central California, San Joaquin Valley (Jan-Feb 2013) and in Houston (Sep 2013). TETHERSONDE RESULTS: The NO2-sonde was deployed on the Millersville University tethersonde balloon along with other instruments measuring trace gases and aerosols included in its payload. Development of the boundary layer can be seen in Figure 7 with ascending profiles (Black) and descending profiles (Blue). All profiles are shown for the same vertical scale (0-700 m) and NO2 is shown here in arbitrary units. AIRCRAFT RESULTS: The NO2-sonde was also deployed for several flights on the UMD aircraft. Figure 6 shows the NO2-sonde profile (blue) with Cavity Ring Down Spectroscopy (CRDS) NO2 (red). The agreement in vertical profile shape is excellent, note the NO2-sonde has a noisier signal due to higher temporal sampling rate (1-sec) than the CRDS. 15 JAN – 15 FEB 2013: CENTRAL CALIFORNIA, San Joaquin Valley SEPTEMBER 2013: HOUSTON, TX The NO2-sonde will be deployed in both of the upcoming DISCOVER-AQ campaigns. In California the NO2-sonde will be used with tethersonde balloon and onboard for some of spiral profile flights. Additionally the NO2-sonde data will be compared to various ground-based data. The aircraft will spiral over the 6 key sites. Tethersonde profiles will be combined with aircraft profiles to span surface, boundary layer and free troposphere. Figure 3, 4, 5 (from left to right). Schematic of NO2-sonde internal mechanism (left), photos of NO2-sonde preparation (center), and a photo of an NO2-sonde launch (right). The KNMI NO2-sondes use chemiluminescence with a luminol solution (Figure 3, 4) to measure variations in concentration of NO2 in the boundary layer and free troposphere with high vertical resolution that OMI cannot detect. Photons are detected with a photodiode array and resulting currents are converted to voltages from the seeing and blind channels. With these voltages, measured temperature information, dark current corrections, and individual sonde characteristics the NO2 concentration can be derived. The NO2-sonde can be used via traditional balloon-borne launches (Figure 5), onboard an aircraft and with a tethersonde balloon (Section 4). The NO2-sonde yields 1-sec data, where the vertical resolution depends on the method of deployment and associated ascent rate. The sonde uses a housing very similar to an ozonesonde and if balloon-launched it is coupled with a radiosonde for measuring temperature and pressure as well as tracking purposes. As the NO2-sonde is still in development it needs to be deployed in conjunction with other NO2-measurements to derive absolute NO2 concentrations. The DISCOVER-AQ campaigns afford the opportunity for comparison with a wide range of NO2-measuring instruments (see Section 5). Figure 1. OMI NO2 (DOMINO) tropospheric (left), total column (right) for 20 July 2011 Issues for OMI NO2 Retrieval: 1) Profile Shape, 2) Aerosol Interference, 3) Impact of Surface Albedo Profile Shape: MAXDOAS and Models NO2- Sonde OMI NO2 Retrieval Figure 7. NO2 vertical profiles from the sonde onboard the tethersonde 20 July 2011. 4b. DISCOVER-AQ Tethersonde: NO2-sonde SENSITIVITY EXPERIMENTS: As part of a European ACTRIS campaign (Aerosols, Clouds, and Trace gases Research InfraStructure Network; www.actris.net), a side-by-side intercomparison experiment was carried out for NO2 instruments including five NO2-sondes at Hohenpießenberg from 12-16 November 2012. The NO2-sondes underwent a series of bench tests with controlled zero air, O3, HNO3, NH3, NO, and NO2 concentrations. The NO2-sonde was found to be insensitive to HNO3 and NH3. Results for linearity tests of variations in NO2 concentration are now being analyzed. Experiment Setup: Aircraft + 6 primary ground sites Ground-based CA Air Resources Board air quality monitors PANDORA (J. Herman) Aircraft-based (300m up through free-troposphere) NO2 Chemiluminesence (NCAR, A. Weinheimer) NO2 TD-LIF (UC-Berkeley, R. Cohen) Tethersonde (ground to 800m) NO/NOx Analyzer (Millersville University) NO2-sonde (KNMI) Figure 6. NO2-sonde profile compared to UMD NO2 from CRDS (left) and photo of NO2-sonde in UMD aircraft (right). yellow Figure 8. Map of key California measurement sites including tethersonde site (red star) and aircraft base (blue circle). The yellow dashed line indicates the general flight pattern. Figure 2. Example of profile shape comparison: NO2- sonde and model profiles (TM4) for measurements made at Cabauw, NL (black circle). Here the model underestimates the near- surface gradient of NO2. SUMMARY: Using a combination of ground-based and airborne platforms, measurements of aerosols and trace gases including O3, NO2, and CH2O will be made on a varying horizontal and vertical scales to explore correlations between surface and (satellite-based) column data and to identify how vertical information can best be used to improve interpretation of satellite column data (ex. OMI) which has little to no vertical sensitivity (See: http://discover-aq.larc.nasa.gov). Step 1: Compare NO2-sonde profiles to model-derived and/or MAXDOAS profiles to improve understanding of profiles using the higher vertical resolution NO2-sonde data; Step 2: Use improved profile shape knowledge to update a priori information about NO2 vertical distribution in the OMI retrieval. NASA P3-B Millersville Tethersonde