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Simultaneous Measurements of HONO and NO2 using Incoherent Broadband Cavity Enhanced Absorption Spectroscopy

This study presents a portable instrument for simultaneous measurements of HONO and NO2 using Incoherent Broadband Cavity Enhanced Absorption Spectroscopy. The instrument design, calibration methods, and field application results are discussed in detail.

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Simultaneous Measurements of HONO and NO2 using Incoherent Broadband Cavity Enhanced Absorption Spectroscopy

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  1. Incoherent broadband cavity-enhanced absorption spectroscopy for simultaneous measurements of HONO and NO2 Min.Qin, Jun.Duan, Renzhi Hu, Wu.Fang, Xue.Lu, Dan.Wang, Pinhua Xie, Wenqing Liu Anhui Institute of Optics and Fine Mechanics, Key Laboratory of Environmental Optics & Technology, Chinese Academy of Science, Hefei,230031,China

  2. Outline • Introduction • IBBCEAS Principle and Setup • Measurements and results • Summary

  3. Introduction Chemistry of HONO The missing sources of HONO in the atmosphere are still under discussion.

  4. Introduction Techniques for atmospheric HONO measurement

  5. IBBCEAS Principle and Setup Intercomparison between LP-DOAS and IBBCEAS LP-DOAS IBBCEAS path length: 1~20 km path length: up to 10 km LP-DOAS instruments: IBBCEAS instruments: ◆ high spatial resolution ◆ weatherproof ◆ compact ◆ sensitive ◆ without calibration ◆ without sampling procedures ◆ sensitive

  6. IBBCEAS Principle and Setup The intensity of the transmitted light[Fielder et. al. 2003]: The absorption coefficient[Fielder et. al. 2003]: For quantitative measurements, the reflectivity, R(= ) , must be known accurately.

  7. IBBCEAS Principle and Setup UV-LED: Ledengin Center wavelength @365 nm FWHM:10nm ILED=900 mA, T=20±0.1 ℃ Spectrometer: QE65000 (Ocean Optics) Wavelength range: 294-410nm Spectral Resolution: 0.4nm Optical cavity: Materail：PFA Inner diameter= 21 mm Rmax：0.99990 (@368.2nm) Length of cavity: 55 cm

  8. IBBCEAS Principle and Setup QE65000 LED mass flowmeter 27cm Pump optical cavity 110cm Optical Fibre 22cm

  9. Measurements and Results LED output & Temperature Peak wavelength shift with temperature：0.052 nm / ℃ Optical intensity change with temperature ：-0.48 % / ℃

  10. Measurements and Results Temperature control of the UV-LED

  11. Measurements and Results Reflectivity calibration Method 1 ： DifferentRayleigh Scattering of He and N2 Method 2: Absorption spectrum of accurate NO2 sample.

  12. Measurements and Results 研究进展 Reflectivity calibration Comparison of the two methods

  13. Measurements and Results Determination of effective cavity length Determine the R Calculate the concentration of pure O2 with purge flows(N2) Calculate the ratio of the retrieved concentration of O2 with and without purge flow In field campaign: The filter and the purge flow are always used deff ≠ the distance between the inlet and outlet. the effective cavity length (deff) can be calculated by multiplying the ratio by the distance between the mirrors(d0)

  14. IBBCEAS Instrument 研究进展 Determination of effective cavity length Case1: purge flow: 0.1 SLM Sampling flow: 3 SLM Case2: purge flow: 0.1 SLM Sampling flow: 1 SLM • deff ≠ the distance between the inlet and outlet. • deff would change due to the different purge flow.

  15. Measurements and Results 研究进展 Determination of effective cavity length Compared with another IBBCEAS instrument without purge flows

  16. Measurements and Results Sample loss NaNO2 + H2SO4 → HONO + NaHSO4 The HONO sample loss of the IBBCEAS instrument was estimated at about 2% Schematic of the HONO production system

  17. Measurements and Results Allan deviation of IBBCEAS The inferred 1σ detection limit of HONO is 80 ppt in 597s

  18. Measurements and Results 研究进展 Field Application CAREBEIJING-NCP 2014 Campaign, 2014.6.26-7.10 Wangdu (N38.68,E115.18; Northern China) , Hebei Province , China Sampling port 12:45 28th June 2014 IBBCEAS instrument 1σ detection limit: HONO 110ppt NO2 200ppt@52s

  19. Measurements and Results 研究进展 Field Application

  20. Measurements and Results Field Application

  21. Measurements and Results Field Application

  22. Summary • Portable design of IBBCEAS Instrument for HONO and NO2 measurements • • The stability of the LED light source • • Two methods for calibration of mirrors reflectivity • • Effective cavity length • • Sampling loss of HONO • • Allan deviation of IBBCEAS • Field applications in Wangdu • • A field intercomparison of HONO and NO2 was carried out

  23. Thank you for your attentions! Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant No. 21190052, 61275151) and the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB05040200, XDB05010500). We would like to thank Julich research center and Peking University for providing data for comparison and researchers and students of Peking University for their help during the 2014 CAREBEIJING-NCP field campaign.

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