HONO retrievals in Beijing and Xianghe

F. Hendrick1, K. Clémer1,*, C. Fayt1, C. Hermans1, Y. Huan1,2, T. Vlemmix1, P. Wang2, and M. Van Roozendael1

1Belgian Institute for Space Aeronomy (IASB-BIRA), Brussels, Belgium

2Institute of Atmospheric Physics, Beijing, China

*Now at Institute of Astrophysics, KU Leuven, Belgium

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 1

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

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

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

DOAS settings

• The following settings are used for the DOAS analysis:

− Fitting window: 337-375 nm

− Fitted species: HONO, NO2, O3, O4, BrO, HCHO, Ring

effect

− HONO XS: Stutz et al. (2000) at 296 K

• For each scan, DSCDoff-axis = SCDoff-axis – SCDzenith of the scan used

by the profiling algorithm

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 5

MAX-DOAS retrieval algorithm

MAXDOAS measurements

LIDORT

O4 DSCDDI

HONO DSCD

DOAS

DSCDDI

Weighting functions

Apriori

Atm: P,TSurface albedoTrace gas: , profileAerosol: 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

Aerosol extinction profile retrievalBeijing 21/01/2009 AM

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 7

Comparison with AERONET data

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 8

HONO vertical profile retrievalBeijing 21/01/2009 AM

A priori:

SH

z

HONO eSH

VCD

with SH = 0.5 km

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 9

Impact of SH on the retrieval (1)Beijing 21/01/2009 AM

A priori Retrieval

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 10

Impact of SH on the retrieval (2)Beijing 21/01/2009

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 11

HONO VCD time-series

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 12

HONO VCD time-series

HONO VCD

Tropospheric NO2 VCD (geometrical approximation)

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 13

HONO and NO2 VCD correlation

Beijing

Xianghe

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 14

Diurnal variation of surface HONO vmr (1)

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 15

Comparison to CAREBeijing2006 data (1)

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 16

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

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 NO2 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:

NO2 profiles retrieval; correlation HONO and NO2 vmr in the 0-200m altitude range

Investigation of the [HONO]/[NO2] ratio

Estimation of the OH production from [HONO] and photolysis rate

NORS/NDACC UV-VIS meeting, Brussels, 3-4 July 2012 18