1. Introduction to Atmospheric Chemistry Measurements-II John Ortega National Center for Atmospheric Research Boulder, CO, USA National Center for Atmospheric Research Boulder, CO USA United States National Science Foundation

2. Outline Review What do we want to measure? Physical, chemical principles Selectivity Detection limits Proxies

3. Some measurement types Spectroscopy (FTIR) Mass spectrometry UV absorption IR absorption Trap (focus) with chromatography Filters

4. Some measurement types of MANY FTIR (Fourier Transform Infrared Spectroscopy) Requires non-symmetric molecule or different atoms Stretching Bending What about CH4? Output provides information on functional groups (OH, COOH, double bonds) and some specific molecules (e.g. H2O). OOC OCOC O OC N NO O Source Path Detector

5. Other IR absorption H2O CH4 H2O Fast (10 Hz) Couple with eddy covariance to get fluxes

6. Mass spectrometry Take in gases into an inlet Reduced pressure Charge molecule (EI or CI) Direct ions using electric fields (lenses) Detector + e- Detector

7. Mass spectrometry

8. GC/MS Element# mass C336 H88 O116 Total Mass60

9. GC/MS Element# mass C336 H88 O116 Total Mass60

10. GC/MS Chromatogram Element# mass C336 H88 O116 Total Mass60

11. Element# mass C336 H88 O116 Total Mass60

12. NO x measurement NO + O3 -> NO2 + h Excess ozone used. Light of particular  is what is detected # of photons detected is proportional to concentration Case 1: Measure total gas stream NO + NO2 Case 2: Pass gas through NO2 converter to convert NO2 to NO Measure both (NO + NO2) = NOx Obtain NO2 by subtracting NOx from total signal Case 3: Pass gas through scrubber to remove all NOx Get zero

13. NO2 converter Headed Mo catalyst Blue light % conversion efficiency – note that when interpreting instrumental data, converting NO2 to NO is not 100% efficient.

14. http://www.wmo.int/pages/prog/arep/gaw/documents/PollackNO2LEDsJAC.pdf Pollack et al., Journal of Atmospheric Chemistry, DOI 10.1007/s10874-011-9184-3, 2011.