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. Techniques for atmospheric HONO measurement
Introduction
Techniques for atmospheric HONO measurement
detection limit(ppt)
time resolution(min)
reference
Direct optical spectroscopic techniques
LP-DOAS
16-100
5-15
Stutz J（2010）
MR-DOAS 84
Alicke B（2003）
IBBCEAS
300 2
Wu T（2014）
TDLAS
200
0.017
Li YQ（2008）
CRDS
5000
0.25
Wang L（2000）
Indirect spectroscopic techniques
CIMS 10
Ren X（2010）
PF/LIF 15 1
Liao W（2006）
Wet chemical techniques
annular denuder-IC 60
Perrino C（1990）
WEDD-IC
5-30
Zellweger C（1999）
WEDD-chemilumine scence
Mikuska P（2008）
ADAMD-IC 8
Takenaka NH（2004）
RWAN-fluorescence 12
5-60
Trebs I（2004）
Mist chamber-IC
Coil-HPLC 5
Zhou X（1999）
LOPAP(Long path absorption photometer) 3
Li X（2014）

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:
◆ without calibration
◆ without sampling procedures
◆ sensitive
◆ high spatial resolution
◆ weatherproof
◆ compact
◆ 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 nm FWHM:10nm
ILED=900 mA, T=20±0.1 ℃
Spectrometer: QE65000 (Ocean Optics)
Wavelength range: nm
Spectral Resolution: 0.4nm
Optical cavity:
Materail：PFA
Inner diameter= 21 mm
Rmax：
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 ：
Different Rayleigh Scattering of He and N2
Method 2:
Absorption spectrum of accurate NO2 sample.

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

14. Determination of effective cavity length
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 Determination of effective cavity length
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
Schematic of the HONO production system
The HONO sample loss of the IBBCEAS instrument was estimated at about 2%

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,
Wangdu (N38.68,E115.18; Northern China) , Hebei Province , China
12:45 28th June 2014
IBBCEAS
instrument
Sampling port
1σ detection limit:
HONO 110ppt NO2

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 , ) and the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB , XDB ). 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.