ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-14-11149-2014 Evaluation of tropospheric SO<sub>2</sub> retrieved from MAX-DOAS measurements in Xianghe, China Wang T. 1 2 Hendrick F. 2 Wang P. 1 Tang G. 1 Clémer K. 2 3 Yu H. 2 Fayt C. 2 Hermans C. 2 Gielen C. 2 Müller J.-F. 2 Pinardi G. 2 Theys N. 2 Brenot H. 2 Van Roozendael M. 2 Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China Belgian Institute for Space Aeronomy, Brussels, Belgium now at: Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Leuven, Belgium 23 10 2014 14 20 11149 11164 Copyright: © 2014 T. Wang et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/14/11149/2014/acp-14-11149-2014.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/14/11149/2014/acp-14-11149-2014.pdf

Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of sulfur dioxide (SO<sub>2</sub>) have been performed at the Xianghe station (39.8° N, 117.0° E) located at ~ 50 km southeast of Beijing from March 2010 to February 2013. Tropospheric SO<sub>2</sub> vertical profiles and corresponding vertical column densities (VCDs), retrieved by applying the optimal estimation method to the MAX-DOAS observations, have been used to study the seasonal and diurnal cycles of SO<sub>2</sub>, in combination with correlative measurements from in situ instruments, as well as meteorological data. A marked seasonality was observed in both SO<sub>2</sub> VCD and surface concentration, with a maximum in winter (February) and a minimum in summer (July). This can be explained by the larger emissions in winter due to the domestic heating and, in case of surface concentration, by more favorable meteorological conditions for the accumulation of SO<sub>2</sub> close to the ground during this period. Wind speed and direction are also found to be two key factors in controlling the level of the SO<sub>2</sub>-related pollution at Xianghe. In the case of east or southwest wind, the SO<sub>2</sub> concentration does not change significantly with the wind speed, since the city of Tangshan and heavy polluting industries are located to the east and southwest of the station, respectively. In contrast, when wind comes from other directions, the stronger the wind, the less SO<sub>2</sub> is observed due to a more effective dispersion. Regarding the diurnal cycle, the SO<sub>2</sub> amount is larger in the early morning and late evening and lower at noon, in line with the diurnal variation of pollutant emissions and atmospheric stability. A strong correlation with correlation coefficients between 0.6 and 0.9 is also found between SO<sub>2</sub> and aerosols in winter, suggesting that anthropogenic SO<sub>2</sub>, through the formation of sulfate aerosols, contributes significantly to the total aerosol content during this season. The observed diurnal cycles of MAX-DOAS SO<sub>2</sub> surface concentration are also in very good agreement (correlation coefficient close to 0.9) with those from collocated in situ data, indicating the good reliability and robustness of our retrieval.

 European Commission NORS - Demonstration Network Of ground-based Remote Sensing Observations in support of the GMES Atmospheric Service (284421) References Bobrowski, N. and Platt, U.: SO<sub>2</sub> / BrO ratios studied in five volcanic plumes, J. Volcanol. Geotherm. Res., 166, 147–160, 2007. Bobrowski, N., von Glasow, R., Aiuppa, A., Inguaggiato, S., Louban, I., Ibrahim, O. W., and Platt, U.: Reactive halogen chemistry in volcanic plumes, J. Geophys. Res., 112, D06311, <a href="http://dx.doi.org/10.1029/2006JD007206">https://doi.org/10.1029/2006JD007206</a>, 2007. Bogumil, K., Orphal, J., Homann, T., Voigt, S., Spietz, P., Fleischmann, O. C., Vogel, A., Hartmann, M., Bovensmann, H., Frerik, J., and Burrows, J. P.: Measurements of molecular absorption spectra with the SCIAMACHY Pre-Flight Model: Instrument characterization and reference spectra for atmospheric remote sensing in the 230–2380 nm region, J. Photoch. Photobio. A, 157, 167–184, 2003. Boynard, A., Clerbaux, C., Clarisse, L., Safieddine, S., Pommier, M., Van Damme, M., Bauduin, S., Oudot, C., Hadji-Lazaro, J., Hurtmans, D., and Coheur, P.-F.: First simultaneous space measurements of atmospheric pollutants in the boundary layer from IASI: a case study in the North China Plain, Geophys. Res. Lett., 41, 645–651, <a href="http://dx.doi.org/10.1002/2013GL058333">https://doi.org/10.1002/2013GL058333</a>, 2014. Brinksma, E. J., Pinardi, G., Volten, H., Braak, R., Richter, A., Schonhardt, A., van Roozendael, M., Fayt, C., Hermans, C., Dirksen, R. J., Vlemmix, T., Berkhout, A. J. C., Swart, D. P. J., Oetjen, H., Wittrock, F., Wagner, T., Ibrahim, O. W., de Leeuw, G., Moerman, M., Curier, R. L., Celarier, E. A., Cede, A., Knap, W. H., Veefkind, J. P., Eskes, H. J., Allaart, M., Rothe, R., Piters, A. J. M., and Levelt, P. F.: The 2005 and 2006 DANDELIONS NO<sub>2</sub> and aerosol intercomparison campaigns, J. Geophys. Res., 113, D16S46, <a href="http://dx.doi.org/10.1029/2007jd008808">https://doi.org/10.1029/2007jd008808</a>, 2008. Cachorro, V. E., Durán, P., Vergaz, R., and de Frutos, A. M.: Measurements of the atmospheric turbidity of the north-centre continental area in Spain: Spectral aerosol optical depth and Ångström turbidity parameters, J. Aerosol Sci., 31, 687–702, 2000. Chan, C. K. and Yao, X.: Air pollution in mega cities in China, Atmos. Environ., 42, 1–42, 2008. Chance, K. V. and Spurr, R. J.: Ring effect studies: Rayleigh scattering, including molecular parameters for rotational Raman scattering, and the Fraunhofer spectrum, Appl. Optics, 36, 5224–5230, 1997. Clémer, K., Van Roozendael, M., Fayt, C., Hendrick, F., Hermans, C., Pinardi, G., Spurr, R., Wang, P., and De Mazière, M.: Multiple wavelength retrieval of tropospheric aerosol optical properties from MAXDOAS measurements in Beijing, Atmos. Meas. Tech., 3, 863–878, <a href="http://dx.doi.org/10.5194/amt-3-863-2010">https://doi.org/10.5194/amt-3-863-2010</a>, 2010. Eisinger, M. and Burrows, J. P.: Tropospheric sulfur dioxide observed by the ERS-2/GOME instrument, Geophys. Res. Lett., 25, 4177–4180, <a href="http://dx.doi.org/10.1029/1998GL900128">https://doi.org/10.1029/1998GL900128</a>, 1998. Fioletov, V. E., McLinden, C. A., Krotkov, N., Yang, K., Loyola, D. G., Valks, P., Theys, N., Van Roozendael, M., Nowlan, C. R., Chance, K., Liu, X., Lee, C., and Martin, R. V.: Application of OMI, SCIAMACHY, and GOME-2 satellite SO<sub>2</sub> retrievals for detection of large emission sources, J. Geophys. Res.-Atmos., 118, 11399–11418, <a href="http://dx.doi.org/10.1002/jgrd.50826">https://doi.org/10.1002/jgrd.50826</a>, 2013. Fleischmann, O. C., Hartmann, M., Burrows, J. P., and Orphal, J.: New ultraviolet absorption cross-sections of BrO at atmospheric temperatures measured by time-windowing Fourier transform spectroscopy, J. Photoch. Photobio. A: Chemistry, 168, 117–132, 2004. Frieß, U., Monks, P. S., Remedios, J. J., Rozanov, A., Sinreich, R., Wagner, T., and Platt, U.: MAX-DOAS O<sub>4</sub> measurements: A new technique to derive information on atmospheric aerosols: 2. Modeling studies, J. Geophys. Res., 111, D14203, <a href="http://dx.doi.org/10.1029/2005jd006618">https://doi.org/10.1029/2005jd006618</a>, 2006. Frieß, U., Sihler, H., Sander, R., Pöhler, D., Yilmaz, S., and Platt, U.: The vertical distribution of BrO and aerosols in the Arctic: Measurements by active and passive differential optical absorption spectroscopy, J. Geophys. Res., 116, D00R04, <a href="http://dx.doi.org/10.1029/2011JD015938">https://doi.org/10.1029/2011JD015938</a>, 2011. Frins, E., Osorio, M., Casaballe, N., Belsterli, G., Wagner, T., and Platt, U.: DOAS-measurement of the NO<sub>2</sub> formation rate from NO<i><sub>x</sub></i> emissions into the atmosphere, Atmos. Meas. Tech., 5, 1165–1172, <a href="http://dx.doi.org/10.5194/amt-5-1165-2012">https://doi.org/10.5194/amt-5-1165-2012</a>, 2012. Galle, B., Johansson, M., Rivera, C., Zhang, Y., Kihlman, M., Kern, C., Lehmann, T., Platt, U., Arellano, S., and Hidalgo, S.: Network for Observation of Volcanic and Atmospheric Change (NOVAC)-A global network for volcanic gas monitoring: Network layout and instrument description, J. Geophys. Res., 115, D05304, <a href="http://dx.doi.org/10.1029/2009JD011823">https://doi.org/10.1029/2009JD011823</a>, 2010. Gauderman, W. J., McConnell, R., Gilliland, F., London, S., Thomas, D., Avol, E., Vora, H., Berhane, K., Rappaport, E. B., and Lurmann, F.: Association between air pollution and lung function growth in southern California children, Am. J. Resp. Crit. Care., 162, 1383–1390, 2000. Grainger, J. and Ring, J.: Anomalous Fraunhofer line profiles, Nature, 193, p. 762, 1962. Großmann, K., Frieß, U., Peters, E., Wittrock, F., Lampel, J., Yilmaz, S., Tschritter, J., Sommariva, R., von Glasow, R., Quack, B., Krüger, K., Pfeilsticker, K., and Platt, U.: Iodine monoxide in the Western Pacific marine boundary layer, Atmos. Chem. Phys., 13, 3363–3378, <a href="http://dx.doi.org/10.5194/acp-13-3363-2013">https://doi.org/10.5194/acp-13-3363-2013</a>, 2013. Hönninger, G., von Friedeburg, C., and Platt, U.: Multi axis differential optical absorption spectroscopy (MAX-DOAS), Atmos. Chem. Phys., 4, 231–254, <a href="http://dx.doi.org/10.5194/acp-4-231-2004">https://doi.org/10.5194/acp-4-231-2004</a>, 2004. Heckel, A., Richter, A., Tarsu, T., Wittrock, F., Hak, C., Pundt, I., Junkermann, W., and Burrows, J. P.: MAX-DOAS measurements of formaldehyde in the Po-Valley, Atmos. Chem. Phys., 5, 909–918, <a href="http://dx.doi.org/10.5194/acp-5-909-2005">https://doi.org/10.5194/acp-5-909-2005</a>, 2005. Hendrick, F., Barret, B., Van Roozendael, M., Boesch, H., Butz, A., De Mazière, M., Goutail, F., Hermans, C., Lambert, J.-C., Pfeilsticker, K., and Pommereau, J.-P.: Retrieval of nitrogen dioxide stratospheric profiles from ground-based zenith-sky UV-visible observations: validation of the technique through correlative comparisons, Atmos. Chem. Phys., 4, 2091–2106, <a href="http://dx.doi.org/10.5194/acp-4-2091-2004">https://doi.org/10.5194/acp-4-2091-2004</a>, 2004. Hendrick, F., Müller, J.-F., Clémer, K., Wang, P., De Mazière, M., Fayt, C., Gielen, C., Hermans, C., Ma, J. Z., Pinardi, G., Stavrakou, T., Vlemmix, T., and Van Roozendael, M.: Four years of ground-based MAX-DOAS observations of HONO and NO<sub>2</sub> in the Beijing area, Atmos. Chem. Phys., 14, 765–781, <a href="http://dx.doi.org/10.5194/acp-14-765-2014">https://doi.org/10.5194/acp-14-765-2014</a>, 2014. Hermans, C., Vandaele, A., Fally, S., Carleer, M., Colin, R., Coquart, B., Jenouvrier, A., and Merienne, M.-F.: Absorption cross-section of the collision-induced bands of oxygen from the UV to the NIR, in: Weakly interacting molecular pairs: unconventional absorbers of radiation in the atmosphere, Springer, 193–202, 2003. Holben, B., Eck, T., Slutsker, I., Tanre, D., Buis, J., Setzer, A., Vermote, E., Reagan, J., Kaufman, Y., and Nakajima, T.: AERONET-A federated instrument network and data archive for aerosol characterization, Remote Sens. Environ., 66, 1–16, 1998. Irie, H., Takashima, H., Kanaya, Y., Boersma, K. F., Gast, L., Wittrock, F., Brunner, D., Zhou, Y., and Van Roozendael, M.: Eight-component retrievals from ground-based MAX-DOAS observations, Atmos. Meas. Tech., 4, 1027–1044, <a href="http://dx.doi.org/10.5194/amt-4-1027-2011">https://doi.org/10.5194/amt-4-1027-2011</a>, 2011. Krotkov, N. A., Carn, S. A., Krueger, A. J., Bhartia, P. K., and Yang, K.: Band Residual Difference Algorithm for Retrieval of SO<sub>2</sub> From the Aura Ozone Monitoring Instrument (OMI), IEEE, Trans. Geosci. Remote Sens., 44, 1259–1266, 2006. Lee, C., Richter, A., Lee, H., Kim, Y. J., Burrows, J. P., Lee, Y. G., and Choi, B. C.: Impact of transport of sulfur dioxide from the Asian continent on the air quality over Korea during May 2005, Atmos. Environ., 42, 1461–1475, 2008. Lee, C., Martin, R. V., van Donkelaar, A., O'Byrne, G., Krotkov, N., Richter, A., Huey, L. G., and Holloway, J. S.: Retrieval of vertical columns of sulfur dioxide from SCIAMACHY and OMI: Air mass factor algorithm development, validation, and error analysis, J. Geophys. Res., 114, D22303, <a href="http://dx.doi.org/10.1029/2009JD012123">https://doi.org/10.1029/2009JD012123</a>, 2009. Lee, C., Martin, R. V., van Donkelaar, A., Lee, H., Dickerson, R. R., Hains, J. C., Krotkov, N., Richter, A., Vinnikov, K., and Schwab, J. J.: SO<sub>2</sub> emissions and lifetimes: Estimates from inverse modeling using in situ and global, space – based(SCIAMACHY and OMI) observations, J. Geophys. Res., 116, D06304, <a href="http://dx.doi.org/10.1029/2010JD014758">https://doi.org/10.1029/2010JD014758</a>, 2011. Li, C., Marufu, L. T., Dickerson, R. R., Li, Z., Wen, T., Wang, Y., Wang, P., Chen, H., and Stehr, J. W.: In situ measurements of trace gases and aerosol optical properties at a rural site in northern China during East Asian Study of Tropospheric Aerosols: An International Regional Experiment 2005, J. Geophys. Res., 112, D22S04, <a href="http://dx.doi.org/10.1029/2006JD007592">https://doi.org/10.1029/2006JD007592</a>, 2007. Lin, W., Xu, X., Ge, B., and Liu, X.: Gaseous pollutants in Beijing urban area during the heating period 2007–2008: variability, sources, meteorological, and chemical impacts, Atmos. Chem. Phys., 11, 8157–8170, <a href="http://dx.doi.org/10.5194/acp-11-8157-2011">https://doi.org/10.5194/acp-11-8157-2011</a>, 2011. Lu, Z., Streets, D. G., Zhang, Q., Wang, S., Carmichael, G. R., Cheng, Y. F., Wei, C., Chin, M., Diehl, T., and Tan, Q.: Sulfur dioxide emissions in China and sulfur trends in East Asia since 2000, Atmos. Chem. Phys., 10, 6311–6331, <a href="http://dx.doi.org/10.5194/acp-10-6311-2010">https://doi.org/10.5194/acp-10-6311-2010</a>, 2010. Ma, J. Z., Xu, X. B., Zhao, C. S., and Yan, P.: A review of atmospheric chemistry research in China: Photochemical smog, haze pollution, and gas-aerosol interactions, Adv. Atmos. Sci., 29, 1006–1026, 2012. Ma, J. Z., Beirle, S., Jin, J. L., Shaiganfar, R., Yan, P., and Wagner, T.: Tropospheric NO<sub>2</sub> vertical column densities over Beijing: results of the first three years of ground-based MAX-DOAS measurements (2008–2011) and satellite validation, Atmos. Chem. Phys., 13, 1547–1567, <a href="http://dx.doi.org/10.5194/acp-13-1547-2013">https://doi.org/10.5194/acp-13-1547-2013</a>, 2013. Meller, R. and Moortgat, G. K.: Temperature dependence of the absorption cross sections of formaldehyde between 223 and 323 K in the wavelength range 225–375 nm, J. Geophys. Res., 105, 7089–7101, 2000. Meng, X., Wang, P., Wang, G., Yu, H., and Zong, X.: Variation and transportation characteristics of SO<sub>2</sub> in winter over Beijing and its surrounding areas, Climatic and Environmental Research (in Chinese), 14, 309–317, 2009. Nowlan, C. R., Liu, X., Chance, K. V., Cai, Z., Kurosu, T. P., Lee, C., and Martin, R. V.: Retrievals of sulfur dioxide from the Global Ozone Monitoring Experiment 2 (GOME-2) using an optimal estimation approach: Algorithm and initial validation, J. Geophys. Res., 116, D18301, <a href="http://dx.doi.org/10.1029/2011JD015808">https://doi.org/10.1029/2011JD015808</a>, 2011. Platt, U. and Stutz, J.: Differential Optical Absorption Spectroscopy (DOAS): Principles and applications, ISBN 978-3-540-21193-8, Springer, Berlin-Heidelberg, 2008. Puķīte, J., Kühl, S., Deutschmann, T., Platt, U., and Wagner, T.: Extending differential optical absorption spectroscopy for limb measurements in the UV, Atmos. Meas. Tech., 3, 631–653, <a href="http://dx.doi.org/10.5194/amt-3-631-2010">https://doi.org/10.5194/amt-3-631-2010</a>, 2010. Rodgers, C. D.: Inverse methods for atmospheric sounding : theory and practice, World Scientific Publishing, Singapore-New Jersey-London-Hong Kong, 2000. Roscoe, H. K., Van Roozendael, M., Fayt, C., du Piesanie, A., Abuhassan, N., Adams, C., Akrami, M., Cede, A., Chong, J., Clémer, K., Friess, U., Gil Ojeda, M., Goutail, F., Graves, R., Griesfeller, A., Grossmann, K., Hemerijckx, G., Hendrick, F., Herman, J., Hermans, C., Irie, H., Johnston, P. V., Kanaya, Y., Kreher, K., Leigh, R., Merlaud, A., Mount, G. H., Navarro, M., Oetjen, H., Pazmino, A., Perez-Camacho, M., Peters, E., Pinardi, G., Puentedura, O., Richter, A., Schönhardt, A., Shaiganfar, R., Spinei, E., Strong, K., Takashima, H., Vlemmix, T., Vrekoussis, M., Wagner, T., Wittrock, F., Yela, M., Yilmaz, S., Boersma, F., Hains, J., Kroon, M., Piters, A., and Kim, Y. J.: Intercomparison of slant column measurements of NO<sub>2</sub> and O<sub>4</sub> by MAX-DOAS and zenith-sky UV and visible spectrometers, Atmos. Meas. Tech., 3, 1629–1646, <a href="http://dx.doi.org/10.5194/amt-3-1629-2010">https://doi.org/10.5194/amt-3-1629-2010</a>, 2010. Tu, F. H., Thornton, D. C., Bandy, A. R., Carmichael, G. R., Tang, Y., Thornhill, K. L., Sachse, G. W., and Blake, D. R.: Long-range transport of sulfur dioxide in the central Pacific, J. Geophys. Res., 109, D15S08, <a href="http://dx.doi.org/10.1029/2003JD004309">https://doi.org/10.1029/2003JD004309</a>, 2004. Vandaele, A., Simon, P. C., Guilmot, J. M., Carleer, M., and Colin, R.: SO<sub>2</sub> absorption cross section measurement in the UV using a Fourier transform spectrometer, J. Geophys. Res., 99, 25599–25605, 1994. Vandaele, A. C., Hermans, C., Simon, P. C., Carleer, M., Colin, R., Fally, S., Merienne, M.-F., Jenouvrier, A., and Coquart, B.: Measurements of the NO<sub>2</sub> absorption cross-section from 42 000 cm<sup>−1</sup> to 10 000 cm<sup>−1</sup> (238–1000 nm) at 220 and 294 K, J. Quant. Spectrosc. Ra., 59, 171–184, 1998. Van Roozendael, M., Loyola, D., Spurr, R., Balis, D., Lambert, J.-C., Livschitz, Y., Valks, P., Ruppert, T., Kenter, P., Fayt, C., and Zehner, C.: Ten years of GOME/ERS-2 total ozone data – The new GOME data processor (GDP) version 4: 1. Algorithm description, J. Geophys. Res., 111, D14311, <a href="http://dx.doi.org/10.1029/2005JD006375">https://doi.org/10.1029/2005JD006375</a>, 2006. Veefkind, J. P., Boersma, K. F., Wang, J., Kurosu, T. P., Krotkov, N., Chance, K., and Levelt, P. F.: Global satellite analysis of the relation between aerosols and short-lived trace gases, Atmos. Chem. Phys., 11, 1255–1267, <a href="http://dx.doi.org/10.5194/acp-11-1255-2011">https://doi.org/10.5194/acp-11-1255-2011</a>, 2011. Vlemmix, T., Piters, A. J. M., Stammes, P., Wang, P., and Levelt, P. F.: Retrieval of tropospheric NO<sub>2</sub> using the MAX-DOAS method combined with relative intensity measurements for aerosol correction, Atmos. Meas. Tech., 3, 1287–1305, <a href="http://dx.doi.org/10.5194/amt-3-1287-2010">https://doi.org/10.5194/amt-3-1287-2010</a>, 2010. Wagner, T., Dix, B., von Friedeburg, C., Friess, U., Sanghavi, S., Sinreich, R., and Platt, U.: MAX-DOAS O<sub>4</sub> measurements: A new technique to derive information on atmospheric aerosols – Principles and information content, J. Geophys. Res., 109, D22205, <a href="http://dx.doi.org/10.1029/2004jd004904">https://doi.org/10.1029/2004jd004904</a>, 2004. Wagner, T., Beirle, S., Brauers, T., Deutschmann, T., Frieß, U., Hak, C., Halla, J. D., Heue, K. P., Junkermann, W., Li, X., Platt, U., and Pundt-Gruber, I.: Inversion of tropospheric profiles of aerosol extinction and HCHO and NO<sub>2</sub> mixing ratios from MAX-DOAS observations in Milano during the summer of 2003 and comparison with independent data sets, Atmos. Meas. Tech., 4, 2685–2715, <a href="http://dx.doi.org/10.5194/amt-4-2685-2011">https://doi.org/10.5194/amt-4-2685-2011</a>, 2011. Wang, T., Nie, W., Gao, J., Xue, L. K., Gao, X. M., Wang, X. F., Qiu, J., Poon, C. N., Meinardi, S., Blake, D., Wang, S. L., Ding, A. J., Chai, F. H., Zhang, Q. Z., and Wang, W. X.: Air quality during the 2008 Beijing Olympics: secondary pollutants and regional impact, Atmos. Chem. Phys., 10, 7603–7615, <a href="http://dx.doi.org/10.5194/acp-10-7603-2010">https://doi.org/10.5194/acp-10-7603-2010</a>, 2010. Wang, T., Wang, P., Yu, H., Zhang, X., Zhou, B., Si, F., Wang, S., Bai, W., Zhou, H., and Zhao, H.: Intercomparison of slant column measurements of NO<sub>2</sub> by ground-based MAX-DOAS, Acta Phys. Sin., 62, 054206, <a href="http://dx.doi.org/10.7498/aps.62.054206">https://doi.org/10.7498/aps.62.054206</a>, 2013. Wang, T., Wang, P., Yu, H., and Sun, L.: Analysis of the characteristics of tropospheric NO<sub>2</sub> in Xianghe based on MAX-DOAS measurement, Climatic and Environmental Research (in Chinese), 19, 51–60, 2014. Wang, W., Chai, F., Zhang, K., Wang, S., Chen, Y., Wang, X., and Yang,Y.: Study on ambient air quality in Beijing for the summer 2008 Olympic Games, Air Qual, Atmos. Health, 1, 31–36, 2008. Wittrock, F., Oetjen, H., Richter, A., Fietkau, S., Medeke, T., Rozanov, A., and Burrows, J. P.: MAX-DOAS measurements of atmospheric trace gases in Ny-Ålesund – Radiative transfer studies and their application, Atmos. Chem. Phys., 4, 955–966, <a href="http://dx.doi.org/10.5194/acp-4-955-2004">https://doi.org/10.5194/acp-4-955-2004</a>, 2004. Wu, F. C., Xie, P. H., Li, A., Chan, K. L., Hartl, A., Wang, Y., Si, F. Q., Zeng, Y., Qin, M., Xu, J., Liu, J. G., Liu, W. Q., and Wenig, M.: Observations of SO<sub>2</sub>2 by mobile DOAS in the Guangzhou eastern area during the Asian Games 2010, Atmos. Meas. Tech., 6, 2277–2292, <a href="http://dx.doi.org/10.5194/amt-6-2277-2013">https://doi.org/10.5194/amt-6-2277-2013</a>, 2013. Xia, X., Zong, X., and Sun, L.: Exceptionally active agricultural fire season in mid-eastern China in June 2012 and its impact on atmospheric environment, J. Geophys. Res. Atmos., 118, 9889–9900, <a href="http://dx.doi.org/10.1002/jgrd.50770">https://doi.org/10.1002/jgrd.50770</a>, 2013. Yan, P., Huang, J., and Draxler, R.: The long-term simulation of surface SO<sub>2</sub> and evaluation of contributions from the different emission sources to Beijing city, Science in China Series D (Earth Sciences), 48, 196–208, 2005. Yan, P., Wang, X., Wang, Z., and Wu, Q.: Analysis of decreases in NO<sub>2</sub> concentrations during Beijing Olympic Games in 2008, Climatic and Environmental Research, 15, 609–615, 2010 (in Chinese). Yang, K., Dickerson, R. R., Carn, S. A., Ge, C., and Wang, J.: First observations of SO<sub>2</sub> from satellite Suomi NPP OMPS: Widespread air pollution events over China, Geophys. Res. Lett., 40, 4957–4962, <a href="http://dx.doi.org/10.1002/grl.50952">https://doi.org/10.1002/grl.50952</a>, 2013. Yu, H., Wang, P., Zong, X., Li, X., and Lü, D.: Change of NO<sub>2</sub> column density over Beijing from satellite measurement during the Beijing 2008 Olympic Games, Chinese Sci. Bull., 55, 308–313, 2010. Yu, X., Zhu, B., and Zhang, M.: Seasonal variability of aerosol optical properties over Beijing, Atmos. Environ., 43, 4095–4101, 2009. Zhang, R., Jing, J., Tao, J., Hsu, S.-C., Wang, G., Cao, J., Lee, C. S. L., Zhu, L., Chen, Z., Zhao, Y., and Shen, Z.: Chemical characterization and source apportionment of PM<sub>2.5</sub> in Beijing: seasonal perspective, Atmos. Chem. Phys., 13, 7053–7074, <a href="http://dx.doi.org/10.5194/acp-13-7053-2013">https://doi.org/10.5194/acp-13-7053-2013</a>, 2013. Zhao, B., Wang, P., Ma, J. Z., Zhu, S., Pozzer, A., and Li, W.: A high-resolution emission inventory of primary pollutants for the Huabei region, China, Atmos. Chem. Phys., 12, 481–501, <a href="http://dx.doi.org/10.5194/acp-12-481-2012">https://doi.org/10.5194/acp-12-481-2012</a>, 2012.