Observations of Formaldehyde and Related Atmospheric Species Using

Observations of Formaldehyde and Related Atmospheric Species Using Multi-Axis Spectroscopy Christopher P. Beekman and Dr. Heather C. Allen Department of Chemistry, and Environmental Sciences Graduate Program The Ohio State University June 19, 2007

Introduction • Understanding the concentrations and distributions of photochemical species and aerosols in an urban air-shed • Combination of spectroscopic and meteorological data with photochemical/radiative transfer models • Important for atmospheric chemistry, health, and climate change modeling

Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) • • Sensitivity to tropospheric absorbers Vertical profiling of trace gases NO 2, O 3, HCHO, HONO, Br. O, Cl. O 2 Ocean Optics USB-2000 – 0. 7 nm resolution – Coupled to 1” telescope w/ multimode fiber – Low power requirements • 8 hours with 12 V battery U. Platt (1994). Air Monitoring by Spectroscopic Techniques. M. W. Sigrist. 27 -84. G. Hönninger, C. Von Friedeburg and U. Platt. Atmospheric Chemistry and Physics 4, 2004.

Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) • Collection of scattered sunlight in the UV-VIS, along different lines of sight • Analysis of raw atmospheric spectra using modified Beer-Lambert law • The most basic measured quantity is Slant Column Density (SCD) • Slant columns at each elevation angle converted to Vertical Column Densities (VCD) • Conversion factor is Air Mass Factor (AMF), calculated using model of solar radiative transfer • UVSPEC/DISORT: lib. Radtran Package SCD VCD B. Mayer and A. Kylling. Atmospheric Chemistry and Physics 5, pp. 1855 -1877, 2005.

Slant Column Density (SCD) Retrieval

Radiative Transfer • Accurate knowledge of vertical structure of atmosphere required • Aerosol optical depth and vertical distribution are key parameters • Inclusion improves the model retrieval of Air Mass Factors

Aerosol Profile Retrieval • Aerosol profiling requires a species with known vertical profile • O 4 is most appropriate in UVVis region • Concentration proportional to [O 2]2 • 12 typical profiles of aerosols simulated within model • Comparison of measured and modeled Air Mass Factors of O 4 yields best match profiles § Greenblatt, G. D. , J. B. Burkholder, A. R. Ravishankara. Journal of Geophysical Research, 95, 1990. § Wagner, T. , B. Dix, C. v. Friedeburg, et al. Journal of Geophysical Research, 109, 2004.

Aerosol Optical Depth Profiles

Volume Mixing Ratios • Vertical Column Densities can be converted to volume mixing ratios • Need to define the mixing height h • Height of lowest layer determined by several methods – Radiosonde data location of 1 st inversion – Height of Aerosol Profile – Box Air Mass Factors Iterative profile variation R. Sinreich, U. Frie. S, T. Wagner, U. Platt. Faraday Discussions 130, 2005.

HCHO • Primarily an oxidation product of other VOCs • Indicator of VOC photochemistry • 1989: 17% of atmospheric HCHO in Columbus attributed to vehicle emissions – • R. Mukund, T. J. Kelly, C. W. Spicer. Atmospheric Environment 30 (20), 1996. 2002: MAX-DOAS measurements of HCHO in Italy – A. Heckel, A. Richter, et al. Atmospheric Chemistry and Physics 5, 2005. HCHO + hv H + HCO H + O 2 HO 2 + NO 2 + OH NO 2 + hv NO + O 2 O 3 A. Heckel, A. Richter, et al. , 2005

HCHO, O 3 and NO 2 • Both days: poor air quality • 5 -30 -07: Strong spike in AM • 5 -31 -07: Elevated NO 2 , possible O 3 suppression during AM • Need more information to characterize regimes

Conclusions and Outlook • MAX-DOAS Effective technique for probing atmospheric photochemistry • HCHO measurements: – 1989: 4. 7 ppb – May and June 2007: 3. 0 ppb • Measurements of O 4: enabled the retrieval of the first vertical profiles of aerosols in central Ohio – Extend to long term, incorporate into photochemical models

Acknowledgements • Professor Heather C. Allen, Allen Lab Members • Professor Katherine Calder, Dr. Hong. Fei Li • Arve Kylling and Bernhard Mayer