Nocturnal surface ozone enhancement over Portugal during winter: Influence of different atmospheric conditions

Pavan S. Kulkarni, Hari Prasad Dasari, Ashish Sharma, D. Bortoli, Rui Salgado, A.M. Silva

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


Four distinct nocturnal surface ozone (NSO) enhancement events were observed, with NSO concentration exceeding 80μg/m3, at multiple ozone (O3) monitoring stations (32 sites) in January, November and December between year 2000–2010, in Portugal. The reasonable explanation for the observed bimodal pattern of surface ozone with enhanced NSO concentration during nighttime has to be transport processes, as the surface ozone production ceases at nighttime. Simultaneous measurements of O3 at multiple stations during the study period in Portugal suggest that horizontal advection alone cannot explain the observed NSO enhancement. Thus, detailed analysis of the atmospheric conditions, simulated with the Weather Research and Forecasting (WRF) model, were performed to evaluate the atmospheric mechanisms responsible for NSO enhancement in the region. Simulations revealed that each event occurred as a result of one or the combination of different atmospheric processes such as, passage of a cold front followed by a subsidence zone; passage of a moving surface trough, with associated strong horizontal wind speed and vertical shear; combination of vertical and horizontal transport at the synoptic scale; formation of a low level jet with associated vertical mixing below the jet stream. The study confirmed that large-scale flow pattern resulting in enhanced vertical mixing in the nocturnal boundary layer, plays a key role in the NSO enhancement events, which frequently occur over Portugal during winter months. © 2016 Elsevier Ltd
Original languageEnglish (US)
Pages (from-to)109-120
Number of pages12
JournalAtmospheric Environment
StatePublished - Sep 24 2016

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The first author (Pavan S Kulkarni) is thankful to Fundação para a Ciência e a Tecnologia for the grant SFRH/BPD/82033/2011. The paper was partially funded through FEDER (ProgramaOperacionalFactores de Competitividade – COMPETE) and National funding through FCT – Fundação para a Ciência e a Tecnologia in the framework of project FCOMP-01-0124-FEDER-014024 (Refa. FCT PTDC/AAC-CLI/114031/2009).The work is co-funded by the European Union through the European Regional Development Fund, included in the COMPETE 2020 (Operational Program Competitiveness and Internationalization) through the ICT project (UID/GEO/04683/2013) with the reference POCI-01-0145-FEDER-007690. Ashish Sharma was supported by National Science Foundation (NSF) grant number: AGS 0934592, the Notre Dame Environmental Change Initiative and the Center for Sustainable Energy. Authors are thankful to APA ( for ozone data, IPMA for meteorological data and NCEP, USA for NNRP/FNL reanalysis data.


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