ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-2021-2009 Modelling trends in OH radical concentrations using generalized additive models Jackson L. S. 1 3 Carslaw N. 1 Carslaw D. C. 2 Emmerson K. M. 1 3 Environment Dept., University of York, York, YO10 5DD, UK Institute for Transport Studies, University of Leeds, Leeds, LS2 9JT, UK now at: School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK 20 03 2009 9 6 2021 2033 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/2021/2009/acp-9-2021-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/2021/2009/acp-9-2021-2009.pdf

During the TORCH campaign a zero dimensional box model based on the Master Chemical Mechanism was used to model concentrations of OH radicals. The model provided a close overall fit to measured concentrations but with some significant deviations. In this research, an approach was established for applying Generalized Additive Models (GAM) to atmospheric concentration data. Two GAM models were fitted to OH radical concentrations using TORCH data, the first using measured OH data and the second using MCM model results. GAM models with five smooth functions provided a close fit to the data with 78% of the deviance explained for measured OH and 83% for modelled OH. The GAM model for measured OH produced substantially better predictions of OH concentrations than the original MCM model results. The diurnal profile of OH concentration was reproduced and the predicted mean diurnal OH concentration was only 0.2% less than the measured concentration compared to 16.3% over-estimation by the MCM model. Photolysis reactions were identified as most important in explaining concentrations of OH. The GAM models combined both primary and secondary pollutants and also anthropogenic and biogenic species to explain changes in OH concentrations. Differences identified in the dependencies of modelled and measured OH concentrations, particularly for aromatic and biogenic species, may help to understand why the MCM model predictions sometimes disagree with measurements of atmospheric species.

 References Baird, C. and Cann, M.: Environmental Chemistry, Freeman, New York, USA, 3rd edn., 154~pp., 2005. Bower, J., Lampert, J., Broughton, G., Stedman, J., Pye, S., Targa, J., Kent, A., and Grice, S.: Air pollution in the UK: 2005, available at: http://www.airquality.co.uk/archive/reports/cat05/0612111534-421_AirPollutionUK2005text.pdf, 2006. Carslaw, D C. and Carslaw, N.: Detecting and characterising small changes in urban nitrogen dioxide concentrations, Atmos. Environ., 41, 4723–4733, 2007. Carslaw, D C., Beevers, S D., and Tate, J E.: Modelling and assessing trends in traffic-related emissions using a generalised additive modelling approach, Atmos. Environ., 41, 5289–5299, 2007. Chatfield, C.: The Analysis of Time Series: An Introduction, Chapman and Hall/CRC, London, UK, 4th edn., 62~pp., 1992. Creasey, D. J., Evans, G. E., Heard, D. E., and Lee, J. D.: Measurements of OH and HO<sub>2</sub> concentrations in the Southern Ocean marine boundary layer, J. Geophys. Res., 108(D15), 4475, doi:10.1029/2002JD003206, 2003. Emmerson, K. M., Carslaw, N., Carpenter, L. J., Heard, D. E., Lee, J. D., and Pilling, M. J.: Urban Atmospheric Chemistry During the PUMA Campaign 1: Comparison of Modelled OH and HO<sub>2</sub> Concentrations with Measurements, J. Atmos. Chem., 52, 143–164, 2005. Emmerson, K. M., Carslaw, N., Carslaw, D. C., Lee, J. D., McFiggans, G., Bloss, W. J., Gravestock, T., Heard, D. E., Hopkins, J., Ingham, T., Pilling, M. J., Smith, S. C., Jacob, M., and Monks, P. S.: Free radical modelling studies during the UK TORCH Campaign in Summer 2003, Atmos. Chem. Phys., 7, 167–181, 2007. European Parliament and Council: Decision No~1600/2002/EC of the European Parliament and of the Council of 22~July~2002 laying down the Sixth Community Environment Action Programme, http://ec.europa.eu/environment/newprg/intro.htm, 2002. Freund, R J. and Wilson, W J.: Regression Analysis: Statistical Modeling of a Response Variable, Academic Press, San Diego and London, 192~pp., 1998. Goldstein, A. H. and Schade, G. W.: Quantifying biogenic and anthropogenic contributions to acetone mixing ratios in a rural environment, Atmos. Environ., 34, 4997–5006, 2000. Hastie, T. J. and Tibshirani, R.: Generalized additive models, Chapman and Hall, London, 352~pp., 1990. Heard, D. E. and Pilling, M. J.: Measurement of OH and HO<sub>2</sub> in the troposphere, Chem. Rev, 103, 5163–5198, 2003. Jenkin, M. E., Saunders, S. M., Wagner, V., and Pilling, M. J.: Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part B): tropospheric degradation of aromatic volatile organic compounds, Atmos. Chem. Phys., 3, 181–193, 2003. Konrad, S., Schmitz, T., Buers, H. J., Houben, N., Mannschreck, K., Mihelcic, D., Musgen, P., Patz, H. W., Holland, F., Hofzumahaus, A., Schafer, H J., Schroder, S., Volz-Thomas, A., Bachmann, K., Schlomski, S., Moortgat, G., and Großmann, D.: Hydrocarbon measurements at Pabstthum during the BERLIOZ campaign and modeling of free radicals, J. Geophys. Res, 108, 8251, doi:10.1029/2001JD000866, 2003. Lee, J. D., Lewis, A. C., Monks, P. S., Jacob, M., Hamilton, J. F., Hopkins, J. R., Watson, N. M., Saxton, J. E., Ennis, C., Carpenter, L. J., Carslaw, N., Fleming, Z., Bandy, B. J., Oram, E. D., Penkett, S. A., Slemr, J., Norton, E., Rickard, A. R., Whalley, L. K., Heard, E. D., Bloss, W. J., Gravestock, T., Smith, S. C., Stanton, J., Pilling, M. J., and Jenkin, M. E.: Ozone photochemistry and elevated isoprene during the UK heatwave of August 2003, Atmos. Environ., 40, 7598–7613, 2006. Lelieveld, J., Butler, T., Crowley, J., Dillon, T., Fischer, H., Ganzeveld, L., Harder, H., Lawrence, M., Martinez, M., Taraborrelli, D., and Williams, J.: Atmospheric oxidation capacity sustained by a tropical forest, Nature, 452, 737–740, 2008. McCullagh, P. and Nelder, J. A.: Generalized Linear Models, Chapman&Hall/CRC, Boca~Raton, Florida, USA, 532~pp., 1989. Montgomery, D. C. and Peck, E. A.: Introduction to Linear Regression Analysis, 4th edn., WileyBlackwell, New York, USA, 117–120, 2006. R Development Core Team: R: A Language and Environment for Statistical Computing, R Foundation for Statistical Computing, Vienna, Austria, 3-900051-07-0, http://www.R-project.org, access: 5the June, 2007, 2007. Reiss, R.: Temporal trends and weekend-weekday differences for benzene and 1,3-butadiene in Houston, Texas, Atmos. Environ., 40, 4711–4724, 2006. Ren, X., Harder, H., Martinez, M., Lesher, R. L., Oliger, A., Simpas, J. B., Brune, W. H., Schwab, J. J., Demerjian, K. L., He, Y., Zhoud, X., and Gao, H.: OH and HO<sub>2</sub> Chemistry in the urban atmosphere of New York City, Atmos. Environ., 37, 3639–3651, 2003. Rohrer, F. and Berresheim, H.: Strong correlation between levels of tropospheric hydroxyl radicals and solar ultraviolet radiation, Nature, 442, 184–187, 2006. Saunders, S. M., Jenkin, M. E., Derwent, R. G., and Pilling, M. J.: Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part A): tropospheric degradation of non-aromatic volatile organic compounds, Atmos. Chem. Phys., 3, 161–180, 2003. Smith, S. C., Lee, J. D., Bloss, W. J., Johnson, G. P., Ingham, T., and Heard, D. E.: Concentrations of OH and HO<sub>2</sub> radicals during NAMBLEX: measurements and steady state analysis, Atmos. Chem. Phys., 6, 1435–1453, 2006. Warneck, P.: Photodissociation of acetone in the troposphere: an algorithm for the quantum yield, Atmos. Environ., 35, 5773–5777, 2001. Westmoreland, E., Carslaw, N., Carslaw, D., Gillah, A., and Bates, E.: Analysis of air quality within a street canyon using statistical and dispersion modelling techniques, Atmos. Environ., 41, 9195–9205, 2007. Wood, S. N.: Generalized Additive Models: An Introduction with R, Chapman and Hall/CRC,Boca Raton, Florida, USA, 154–160, 2006.