1. HONO retrievals in Beijing and Xianghe F. Hendrick 1, K. Clémer 1,*, C. Fayt 1, C. Hermans 1, Y. Huan 1,2, T. Vlemmix 1, P. Wang 2, and M. Van Roozendael 1 1 Belgian Institute for Space Aeronomy (IASB-BIRA), Brussels, Belgium 2 Institute of Atmospheric Physics, Beijing, China *Now at Institute of Astrophysics, KU Leuven, Belgium NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 1

2. Nitrous acid (HONO) in the troposphere HONO is a source of OH radicals through its photolysis, especially in the early morning: HONO + h → OH + NO HONO sources and sinks: Li et al., ACP, 2012 NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 2

3. Why it is important to measure HONO ? Formation mechanisms not well understood and poorly quantified, especially during daytime  Realistic simulations of HONO levels are difficult  Measurements can contribute to improve the modeling of the HONO and OH chemistry HONO measurements are sparse in time because mainly resulting from field campaigns Continuous MAX-DOAS measurements of HONO can be highly valuable NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 3

4. Observation sites Institute of Atmospheric Physics (06/2008 - 04/2009) (03/2010 till now ) NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 4

5. DOAS settings The following settings are used for the DOAS analysis: −Fitting window: 337-375 nm −Fitted species: HONO, NO 2, O 3, O 4, BrO, HCHO, Ring effect −HONO XS: Stutz et al. (2000) at 296 K For each scan, DSCD off-axis = SCD off-axis – SCD zenith of the scan used by the profiling algorithm NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 5

6. MAX-DOAS retrieval algorithm MAXDOAS measurements LIDORT O 4 DSCD DI HONO DSCD DOAS DSCD DI Weighting functions Apriori Atm: P,T Surface albedo Trace gas: , profile Aerosol: optical prop. Optimal estimation Aerosol vertical extinction profiles Tropospheric HONO vertical profiles Clémer et al., AMT, 2010 NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 6

7. Aerosol extinction profile retrieval Beijing 21/01/2009 AM NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 7

8. Comparison with AERONET data NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 8

9. HONO vertical profile retrieval Beijing 21/01/2009 AM A priori: with SH = 0.5 km NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 9

10. Impact of SH on the retrieval (1) Beijing 21/01/2009 AM A prioriRetrieval NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 10

11. Impact of SH on the retrieval (2) Beijing 21/01/2009 NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 11

12. HONO VCD time-series NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 12

13. HONO VCD time-series HONO VCD Tropospheric NO 2 VCD (geometrical approximation) NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 13

14. HONO and NO 2 VCD correlation Beijing Xianghe NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 14

15. Diurnal variation of surface HONO vmr (1) NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 15

16. Comparison to CAREBeijing2006 data (1) NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 16

17. Comparison to CAREBeijing2006 data (2) CAREBeijing2006 HONO measurements at Yufa: in-situ long-path absorption photometry (LOPAP); see Lu et al., ACPD, 2012 NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 17

18. Concluding remarks First HONO retrievals from MAX-DOAS observations at Beijing and Xianghe show promising results  HONO columns larger at Beijing  Good correlation between HONO and NO 2 tropospheric columns, especially in the afternoon  Diurnal variation of HONO vmr in the 0-200m altitude range; Good agreement with CAREBeijing2006 data On-going work:  NO 2 profiles retrieval; correlation HONO and NO 2 vmr in the 0-200m altitude range  Investigation of the [HONO]/[NO 2 ] ratio  Estimation of the OH production from [HONO] and photolysis rate NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 18