Skip to main content
SpringerLink
Log in

Pollutant vertical mixing in the nocturnal boundary layer enhanced by density currents and low-level jets: two representative case studies

  • Research Article
  • Published:
Boundary-Layer Meteorology Aims and scope Submit manuscript

Abstract

Turbulent and intermittent characteristics of the nocturnal boundary layer play an important role in determining the transport, diffusion, and storage of momentum, heat, and atmospheric pollutants. Here we use micrometeorological observations and numerical simulations to analyze two coherent turbulent structures—a density current and a low-level jet (LLJ)—that enhance mixing and intermittent turbulence in the nocturnal boundary layer. We analyze in detail their impact on the distribution of simulated pollutant concentrations. The Weather Research and Forecast (WRF) model is coupled with the Community Multiscale Air Quality photochemical model to simulate the dispersion of pollutants for the density-current and LLJ cases. The terms of the pollutant-concentration budget are then analyzed to quantify the contribution of different atmospheric processes on the net \(\hbox {NO}_2\) and \(\hbox {O}_3\) concentrations. The results show that the WRF model reproduces successfully the essential characteristics observed in the density-current and LLJ cases. The density-current simulation shows turbulent-mixing enhancement in the frontal zone of the density current, leading to significant vertical pollutant diffusion. Results also indicate that the LLJ is able to transport pollutants from the residual layer to the surface layer due to vertical diffusion. In both cases, the main mechanism responsible for pollutant transport is the horizontal advection.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9

Similar content being viewed by others

References

  • Acevedo OC, Moraes OL, Degrazia GA, Medeiros LE (2006) Intermittency and the exchange of scalars in the nocturnal surface layer. Boundary-Layer Meteorol 119(1):41–55

    Article  Google Scholar 

  • Adachi A, Clark W, Hartten L, Gage K, Kobayashi T (2004) An observational study of a shallow gravity current triggered by katabatic flow. Ann Geophys Copernic GmbH 22:3937–3950

    Article  Google Scholar 

  • Balsley BB, Svensson G, Tjernström M (2008) On the scale-dependence of the gradient richardson number in the residual layer. Boundary-Layer Meteorol 127(1):57–72

    Article  Google Scholar 

  • Banks RF, Baldasano JM (2016) Impact of WRF model PBL schemes on air quality simulations over Catalonia, Spain. Sci Total Environ 572:98–113

    Article  Google Scholar 

  • Banks RF, Tiana-Alsina J, Baldasano JM, Rocadenbosch F, Papayannis A, Solomos S, Tzanis CG (2016) Sensitivity of boundary-layer variables to PBL schemes in the WRF model based on surface meteorological observations, lidar, and radiosondes during the HygrA-CD campaign. Atmos Res 176:185–201

    Article  Google Scholar 

  • Banta RM (2008) Stable-boundary-layer regimes from the perspective of the low-level jet. Acta Geophys 56(1):58–87

    Article  Google Scholar 

  • Bhave P, Nolte C, Pleim J, Schwede D, Roselle S (2005) Recent developments in the CMAQ modal aerosol module. In: Proceedings of the models-3 users workshop

  • Blumen W, Grossman R, Piper M (1999) Analysis of heat budget, dissipation and frontogenesis in a shallow density current. Boundary-Layer Meteorol 91(2):281–306

    Article  Google Scholar 

  • Borge R, Santiago JL, de la Paz D, Martín F, Domingo J, Valdés C, Sánchez B, Rivas E, Rozas MT, Lázaro S et al (2018) Application of a short term air quality action plan in Madrid (Spain) under a high-pollution episode-part II: assessment from multi-scale modelling. Sci Total Environ 635:1574–1584

    Article  Google Scholar 

  • Bougeault P, Lacarrère P (1989) Parameterization of orography-induced turbulence in a mesobeta-scale model. Mon Weather Rev 117(8):1872–1890

    Article  Google Scholar 

  • Bravo M, Mira T, Soler M, Cuxart J (2008) Intercomparison and evaluation of MM5 and Meso-NH mesoscale models in the stable boundary layer. Boundary-Layer Meteorol 128(1):77–101

    Article  Google Scholar 

  • Bretherton CS, Park S (2009) A new moist turbulence parameterization in the Community Atmosphere Model. J Clim 22(12):3422–3448

    Article  Google Scholar 

  • Byun DW, Ching J et al (1999) Science algorithms of the EPA models-3 community multiscale air quality (CMAQ) modeling system. US Environmental Protection Agency, Office of Research and Development, Washington, DC

    Google Scholar 

  • Chemel C, Staquet C, Largeron Y (2009) Generation of internal gravity waves by a katabatic wind in an idealized alpine valley. Meteorol Atmos Phys 103(1–4):187–194

    Article  Google Scholar 

  • Chen F, Dudhia J (2001) Coupling an advanced land surface-hydrology model with the penn state-ncar MM5 modeling system. Part I: model implementation and sensitivity. Mon Weather Rev 129(4):569–585

    Article  Google Scholar 

  • Conangla L, Cuxart J (2006) On the turbulence in the upper part of the low-level jet: an experimental and numerical study. Boundary-Layer Meteorol 118(2):379–400

    Article  Google Scholar 

  • Coulter RL, Kallistratova MA (2004) Two decades of progress in sodar techniques: a review of 11 isars proceedings. Meteorol Atmos Phys 85(1):3–19

    Google Scholar 

  • Cuxart J (2008) Nocturnal basin low-level jets: an integrated study. Acta Geophys 56(1):100–113

    Article  Google Scholar 

  • Cuxart J, Jiménez M (2007) Mixing processes in a nocturnal low-level jet: an LES study. J Atmos Sci 64(5):1666–1679

    Article  Google Scholar 

  • Cuxart J, Yagüe C, Morales G, Terradellas E, Orbe J, Calvo J, Fernández A, Soler M, Infante C, Buenestado P et al (2000) Stable atmospheric boundary-layer experiment in Spain (SABLES 98): a report. Boundary-Layer Meteorol 96(3):337–370

    Article  Google Scholar 

  • Dudhia J (1989) Numerical study of convection observed during the winter monsoon experiment using a mesoscale two-dimensional model. J Atmos Sci 46(20):3077–3107

    Article  Google Scholar 

  • Ferreres E, Soler M, Terradellas E (2013) Analysis of turbulent exchange and coherent structures in the stable atmospheric boundary layer based on tower observations. Dyn Atmos Oceans 64:62–78

    Article  Google Scholar 

  • Floors R, Vincent CL, Gryning SE, Peña A, Batchvarova E (2013) The wind profile in the coastal boundary layer: wind lidar measurements and numerical modelling. Boundary-Layer Meteorol 147(3):469–491

    Article  Google Scholar 

  • Freedman FR, Bornstein RD (1998) Study of the spacial and temporal structure of turbulence in the nocturnal residual layer. In: Gryning SE, Chaumerliac N (eds) Air pollution modeling and its application XII. NATO \(\bullet \) Challenges of modern society, vol 22. Springer, Boston

  • Garratt JR (1994) The atmospheric boundary layer. Cambridge atmospheric and space science series. Cambridge University Press, Cambridge

    Google Scholar 

  • Gonçalves M, Jiménez-Guerrero P, Baldasano JM (2009) Contribution of atmospheric processes affecting the dynamics of air pollution in south-western europe during a typical summertime photochemical episode. Atmos Chem Phys 9(3):849–864

    Article  Google Scholar 

  • Grell GA, Dévényi D (2002) A generalized approach to parameterizing convection combining ensemble and data assimilation techniques. Geophys Res Lett 29(14):38–1

    Article  Google Scholar 

  • Hong SY, Noh Y, Dudhia J (2006) A new vertical diffusion package with an explicit treatment of entrainment processes. Mon Weather Rev 134(9):2318–2341

    Article  Google Scholar 

  • Hong C, Zhang Q, Zhang Y, Tang Y, Tong D, He K (2017) Multi-year downscaling application of two-way coupled WRF v3. 4 and CMAQ v5. 0.2 over east Asia for regional climate and air quality modeling: model evaluation and aerosol direct effects. Geosci Model Dev 10(6):2447–2470

  • Hu XM, Nielsen-Gammon JW, Zhang F (2010) Evaluation of three planetary boundary layer schemes in the WRF model. J Appl Meteorol Climatol 49(9):1831–1844

    Article  Google Scholar 

  • Hu XM, Doughty DC, Sanchez KJ, Joseph E, Fuentes JD (2012) Ozone variability in the atmospheric boundary layer in Maryland and its implications for vertical transport model. Atmos Environ 46:354–364

    Article  Google Scholar 

  • Hu XM, Klein PM, Xue M, Zhang F, Doughty DC, Forkel R, Joseph E, Fuentes JD (2013) Impact of the vertical mixing induced by low-level jets on boundary layer ozone concentration. Atmos Environ 70:123–130

    Article  Google Scholar 

  • Hu J, Chen J, Ying Q, Zhang H (2016) One-year simulation of ozone and particulate matter in China using WRF/CMAQ modeling system. Atmos Chem Phys 16(16):10,333–10,350

    Article  Google Scholar 

  • Hu J, Li X, Huang L, Ying Q, Zhang Q, Zhao B, Wang S, Zhang H (2017) Ensemble prediction of air quality using the WRF/CMAQ model system for health effect studies in China. Atmos Chem Phys 17(21):13,103–13,118

    Article  Google Scholar 

  • Jang JCC, Jeffries HE, Byun D, Pleim JE (1995a) Sensitivity of ozone to model grid resolution. Application of high-resolution regional acid deposition model. Atmos Environ 29(21):3085–3100

    Article  Google Scholar 

  • Jang JCC, Jeffries HE, Tonnesen S (1995b) Sensitivity of ozone to model grid resolution. Detailed process analysis for ozone chemistry. Atmos Environ 29(21):3101–3114

    Article  Google Scholar 

  • Janjić ZI (2002) Nonsingular implementation of the Mellor–Yamada level 2.5 scheme in the NCEP meso model. NCEP office note, vol 437, p 61

  • Janjic ZI (1990) The step-mountain coordinate: physical package. Mon Weather Rev 118(7):1429–1443

    Article  Google Scholar 

  • Li L, Chen C, Huang C, Huang H, Zhang G, Wang Y, Wang H, Lou S, Qiao L, Zhou M et al (2012) Process analysis of regional ozone formation over the Yangtze river delta, China using the community multi-scale air quality modeling system. Atmos Chem Phys 12(22):10,971–10,987

    Article  Google Scholar 

  • Mahrt L (1982) Momentum balance of gravity flows. J Atmos Sci 39(12):2701–2711

    Article  Google Scholar 

  • Mahrt L (1999) Stratified atmospheric boundary layers. Boundary-Layer Meteorol 90(3):375–396

    Article  Google Scholar 

  • Mahrt L (2014) Stably stratified atmospheric boundary layers. Annu Rev Fluid Mech 46:23–45

    Article  Google Scholar 

  • Martínez D, Cuxart J (2009) Assessment of the hydraulic slope flow approach using a mesoscale model. Acta Geophys 57(4):882–903

    Article  Google Scholar 

  • Misenis C, Zhang Y (2010) An examination of sensitivity of WRF/Chem predictions to physical parameterizations, horizontal grid spacing, and nesting options. Atmos Res 97(3):315–334

    Article  Google Scholar 

  • Mlawer EJ, Taubman SJ, Brown PD, Iacono MJ, Clough SA (1997) Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave. J Geophys Res 102(14):16663–16682

    Article  Google Scholar 

  • Nakanishi M, Niino H (2006) An improved Mellor–Yamada level-3 model: its numerical stability and application to a regional prediction of advection fog. Boundary-Layer Meteorol 119(2):397–407

    Article  Google Scholar 

  • Pleim JE (2007) A combined local and nonlocal closure model for the atmospheric boundary layer. Part I: model description and testing. J Appl Meteorol Climatol 46(9):1383–1395

    Article  Google Scholar 

  • Pleim JE, Chang JS (1992) A non-local closure model for vertical mixing in the convective boundary layer. Atmos Environ A Gen Top 26(6):965–981

    Article  Google Scholar 

  • Prabha TV, Hoogenboom G, Smirnova TG (2011) Role of land surface parameterizations on modeling cold-pooling events and low-level jets. Atmos Res 99(1):147–161

    Article  Google Scholar 

  • Prtenjak MT, Jeričević A, Klaić ZB, Alebić-Juretić A, Bulić IH (2013) Atmospheric dynamics and elevated ozone concentrations in the northern adriatic. Meteorol Appl 20(4):482–496

    Article  Google Scholar 

  • Pugh TA, Ryder J, MacKenzie AR, Moller SJ, Lee JD, Helfter C, Nemitz E, Lowe D, Hewitt CN (2010) Modelling chemistry in the nocturnal boundary layer above tropical rainforest and a generalised effective nocturnal ozone deposition velocity for sub-ppbv NOx conditions. J Atmos Chem 65(2–3):89–110

    Article  Google Scholar 

  • Querol X, Gangoiti G, Mantilla E, Alastuey A, Minguillón MC, Amato F, Reche C, Viana M, Moreno T, Karanasiou A, Rivas I, Pérez N, Ripoll A, Brines M, Ealo M, Pandolfi M, Lee HK, Eun HR, Park YH, Escudero M, Beddows D, Harrison RM, Bertrand A, Marchand N, Lyasota A, Codina B, Olid M, Udina M, Jiménez-Esteve B, Soler MR, Alonso L, Millán M, Ahn KH (2017) Phenomenology of high-ozone episodes in ne Spain. Atmos Chem Phys 17(4):2817–2838

    Article  Google Scholar 

  • Renfrew IA (2004) The dynamics of idealized katabatic flow over a moderate slope and ice shelf. Q J R Meteorol Soc 130(598):1023–1045

    Article  Google Scholar 

  • Román-Cascón C, Yagüe C, Mahrt L, Sastre M, Steeneveld G, Pardyjak E, van de Boer A, Hartogensis O (2015) Interactions among drainage flows, gravity waves and turbulence: a BLLAST case study. Atmos Chem Phys 15(8):12,821–12,865

    Article  Google Scholar 

  • Rotach MW, Vogt R, Bernhofer C, Batchvarova E, Christen A, Clappier A, Feddersen B, Gryning SE, Martucci G, Mayer H, Mitev V, Oke TR, Parlow E, Richner H, Roth M, Roulet YA, Ruffieux D, Salmond JA, Schatzmann M, Voogt JA (2005) BUBBLE—an urban boundary-layer meteorology project. Theor Appl Climatol 81(3):231–261

    Article  Google Scholar 

  • Salmond J, McKendry I (2002) Secondary ozone maxima in a very stable nocturnal boundary layer: observations from the Lower Fraser Valley, BC. Atmos Environ 36(38):5771–5782

    Article  Google Scholar 

  • San José R, Casanova J, Viloria RE, Casanova J (1985) Evaluation of the turbulent parameters of the unstable surface boundary layer outside businger’s range. Atmos Environ (1967) 19(10):1555–1561

    Article  Google Scholar 

  • Shankar U, Bhave P, Vukovich J, Roselle S (2005) Implementation and initial applications of sea salt aerosol emissions and chemistry algorithms in the CMAQ v4.5-aero4 module. In: 4th annual CMAS models-3 users conference, Chapel Hill, NC, pp 26–28

  • Shin HH, Hong SY (2011) Intercomparison of planetary boundary-layer parametrizations in the WRF model for a single day from CASES-99. Boundary-Layer Meteorol 139(2):261–281

    Article  Google Scholar 

  • Siebert H, Wendisch M, Conrath T, Teichmann U, Heintzenberg J (2003) A new tethered balloon-borne payload for fine-scale observations in the cloudy boundary layer. Boundary-Layer Meteorol 106(3):461–482

    Article  Google Scholar 

  • Simpson JE (1999) Gravity currents: in the environment and the laboratory. Cambridge University Press, Cambridge

    Google Scholar 

  • Skamarock WC, Klemp J, Dudhia J, Gill D, Barker D, Wang W, Powers J (2008) A description of the advanced research WRF version 3. NCAR technical notes-475+ str. National Center for Atmospheric Research (NCAR)

  • Smith EN, Gibbs JA, Fedorovich E, Klein PM (2018) WRF model study of the great plains low-level jet: effects of grid spacing and boundary layer parameterization. J Appl Meteorol Climatol 57(10):2375–2397. https://doi.org/10.1175/JAMC-D-17-0361.1

    Article  Google Scholar 

  • Soler M, Infante C, Buenestado P, Mahrt L (2002) Observations of nocturnal drainage flow in a shallow gully. Boundary-Layer Meteorol 105(2):253–273

    Article  Google Scholar 

  • Soler M, Udina M, Ferreres E (2014) Observational and numerical simulation study of a sequence of eight atmospheric density currents in northern Spain. Boundary-Layer Meteorol 153(2):195–216

    Article  Google Scholar 

  • Storm B, Dudhia J, Basu S, Swift A, Giammanco I (2009) Evaluation of the weather research and forecasting model on forecasting low-level jets: implications for wind energy. Wind Energy 12(1):81–90

    Article  Google Scholar 

  • Stull RB (1988) An introduction to boundary layer meteorology. Kluwer Academic Publishers, Dordrecht

    Book  Google Scholar 

  • Sukoriansky S, Galperin B, Perov V et al (2006) A quasi-normal scale elimination model of turbulence and its application to stably stratified flows. Nonlinear Process Geophys 13(1):9–22

    Article  Google Scholar 

  • Sun J, Burns SP, Lenschow DH, Banta R, Newsom R, Coulter R, Frasier S, Ince T, Nappo C, Cuxart J et al (2002) Intermittent turbulence associated with a density current passage in the stable boundary layer. Boundary-Layer Meteorol 105(2):199–219

    Article  Google Scholar 

  • Sun J, Lenschow DH, Burns SP, Banta RM, Newsom RK, Coulter R, Frasier S, Ince T, Nappo C, Balsley BB et al (2004) Atmospheric disturbances that generate intermittent turbulence in nocturnal boundary layers. Boundary-Layer Meteorol 110(2):255–279

    Article  Google Scholar 

  • Terradellas E, Morales G, Cuxart J, Yagüe C (2001) Wavelet methods: application to the study of the stable atmospheric boundary layer under non-stationary conditions. Dyn Atmos Oceans 34(2):225–244

    Article  Google Scholar 

  • Terradellas E, Soler M, Ferreres E, Bravo M (2005) Analysis of oscillations in the stable atmospheric boundary layer using wavelet methods. Boundary-Layer Meteorol 114(3):489–518

    Article  Google Scholar 

  • Thompson G, Rasmussen RM, Manning K (2004) Explicit forecasts of winter precipitation using an improved bulk microphysics scheme. Part I: description and sensitivity analysis. Mon Weather Rev 132(2):519–542

    Article  Google Scholar 

  • Tjernström M, Balsley B, Svensson G, Nappo C (2008) Observations of turbulence in the residual layer. In: 18th symposium on boundary layers and turbulence

  • Udina M, Soler MR, Arasa R (2012) Effects of nocturnal thermal circulation and boundary layer structure on pollutant dispersion in complex terrain areas: a case study. Int J Environ Pollut 48(1):47–59

    Article  Google Scholar 

  • Udina M, Soler MR, Viana S, Yagüe C (2013) Model simulation of gravity waves triggered by a density current. Q J R Meteorol Soc 139(672):701–714

    Article  Google Scholar 

  • Viana S, Yagüe C, Maqueda G, Morales G (2007) Study of the surface pressure fluctuations generated by waves and turbulence in the nocturnal boundary layer during SABLES2006 field campaign. Física de la Tierra 19:55–71

    Google Scholar 

  • Viana S, Yagüe C, Maqueda G (2009) Propagation and effects of a mesoscale gravity wave over a weakly-stratified nocturnal boundary layer during the SABLES2006 field campaign. Boundary-Layer Meteorol 133(2):165–188

    Article  Google Scholar 

  • Viana S, Terradellas E, Yagüe C (2010) Analysis of gravity waves generated at the top of a drainage flow. J Atmos Sci 67(12):3949–3966

    Article  Google Scholar 

  • Wang X, Zhang Y, Hu Y, Zhou W, Lu K, Zhong L, Zeng L, Shao M, Hu M, Russell A (2010) Process analysis and sensitivity study of regional ozone formation over the Pearl River Delta, China, during the PRIDE-PRD2004 campaign using the Community Multiscale Air Quality modeling system. Atmos Chem Phys 10(9):4423–4437

    Article  Google Scholar 

  • Wang N, Guo H, Jiang F, Ling Z, Wang T (2015) Simulation of ozone formation at different elevations in mountainous area of Hong Kong using WRF-CMAQ model. Sci Total Environ 505:939–951

    Article  Google Scholar 

  • Yagüe C, Viana S, Maqueda G, Lazcano MF, Morales G, Rees JM (2007) A study on the nocturnal atmospheric boundary layer: SABLES2006. Física de la Tierra 19:37–53

    Google Scholar 

  • Yarwood G, Rao S, Yocke M, Whitten G (2005) Updates to the carbon bond chemical mechanism: CB05. Final report to the US EPA, RT-0400675 8

  • Yus-Díez J, Udina M, Soler MR, Lothon M, Nilsson E, Bech J, Sun J (2019) Nocturnal boundary layer turbulence regimes analysis during the bllast campaign. Atmos Chem Phys 19(14):9495–9514

    Article  Google Scholar 

  • Zhang H, Chen G, Hu J, Chen SH, Wiedinmyer C, Kleeman M, Ying Q (2014) Evaluation of a seven-year air quality simulation using the Weather Research and Forecasting (WRF)/Community Multiscale Air Quality (CMAQ) models in the eastern United States. Sci Total Environ 473:275–285

    Google Scholar 

Download references

Acknowledgements

The work was supported by the Spanish Government through the MINECO Projects CGL2012-37416-C04-04, CGL2015-65627-C3-2-R and CGL2016-81828-REDT.

Author information

Author notes

  1. Miriam Olid

    Present address: Earth Science Department, Barcelona Supercomputing Center (BSC), Barcelona, Spain

  2. Bernat Jiménez-Esteve

    Present address: Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland

Authors and Affiliations

  1. Departament de Física Aplicada - Meteorologia, Universitat de Barcelona, C/ Martí i Franquès, 1, 08028, Barcelona, Spain

    Mireia Udina, Maria Rosa Soler, Miriam Olid, Bernat Jiménez-Esteve & Joan Bech

Authors
  1. Mireia Udina
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Maria Rosa Soler
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Miriam Olid
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Bernat Jiménez-Esteve
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Joan Bech
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Mireia Udina.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Appendix Control Case: Meteorological Analysis

Appendix Control Case: Meteorological Analysis

The meteorological analysis for the control cases corresponding to the night of 17–18 July 2003 is given in Fig. 10. In the control case 1, the concentrations are explored at 1900 UTC (see the purple vertical line in Fig. 10). In the control case 2, the selected comparison time is at 2300 UTC (see brown vertical line in Fig. 10).

Fig. 10
figure 10

Time series from 1800 UTC on 17 July 2003 to 0600 UTC on 18 July 2003 for a air temperature, b wind speed, c wind direction, d specific humidity measured at different levels of the CIBA tower (all averaged over 5-min periods). Vertical lines indicate the selected times: the control case 1 (CC1, purple line), sunset (at around 1952 UTC, black dashed line), and the control case 2 (CC2, brown line)

Full size image

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Udina, M., Soler, M.R., Olid, M. et al. Pollutant vertical mixing in the nocturnal boundary layer enhanced by density currents and low-level jets: two representative case studies. Boundary-Layer Meteorol 174, 203–230 (2020). https://doi.org/10.1007/s10546-019-00483-y

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/s10546-019-00483-y

Keywords

Search

Navigation