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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Jul 2018

Research article | 30 Jul 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Analysis of spatial and temporal patterns of on-road NO2 concentrations in Hong Kong

Ying Zhu1, Ka Lok Chan1,2, Yun Fat Lam3,4, Martin Horbanski5, Denis Pöhler5, Johannes Boll1, Ivo Lipkowitsch1, Sheng Ye1, and Mark Wenig1 Ying Zhu et al.
  • 1Meteorological Institute, Ludwig-Maximilians-Universität München, Munich, Germany
  • 2Remote Sensing Technology Institute, German Aerospace Center (DLR), Oberpfaffenhofen, Germany
  • 3School of Energy and Environment, City University of Hong Kong, Hong Kong
  • 4Guy Carpenter Climate Change Centre, City University of Hong Kong, Hong Kong
  • 5Institute of Environmental Physics, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany

Abstract. In this paper we present an investigation of the spatial and temporal variability of street level concentrations of NO2 in Hong Kong as an example for a densely populated megacity with heavy traffic. For the study we use a combination of open path remote sensing and in-situ measurement techniques that allows us to separate temporal changes and spatial patterns and analyse them separately. Two measurement campaigns have been conducted, one in December 2010 and one in March 2017. Each campaign lasted for a week which allowed us to examine diurnal cycles, weekly patterns as well as spatially resolved long term changes. We combined a long-path Differential Optical Absorption Spectroscopy (DOAS) instrument with a cavity enhanced DOAS and applied several normalizations to the data sets in order to make the different measurement routes comparable. For the analysis of long term changes we used the entire unfiltered data set, for the comparison of spatial patterns we filtered out the accumulation of NO2 when stopping at traffic lights for focusing on the changes of NO2 spatial distribution instead of comparing traffic flow patterns, and for the generation of composite maps the diurnal cycle has been normalized by scaling the mobile data with coinciding citywide path-averaged measurement results.

An overall descending trend from 2010 to 2017 could be observed, consistent with the observations of the ozone monitoring instrument (OMI) and the Environment Protection Department (EPD) air quality monitoring network data. However, long term difference maps show pronounced spatial structures with some areas, e.g. around subway stations, revealing an increasing trend. We could also show, that the weekend effect, which for the most part of Hong Kong shows reduced NO2 concentrations on Sundays and to a lesser degree on Saturdays, is reversed around shopping malls. Our study shows that the spatial differences have to be considered when discussing city-wide trends and can be used to put local point measurements into perspective. The resulting data set provides a better insight into on-road NO2 characteristics in Hong Kong which helps to identify heavily polluted areas and represents a useful database for urban planning and the design of pollution control measures.

Ying Zhu et al.
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Ying Zhu et al.
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Short summary
The manuscript presents an investigation of spatio-temporal variability of street level NO2 in Hong Kong using both mobile cavity enhanced Differential Optical Absorption Spectroscopy (DOAS) and long-path DOAS. Measurements were conducted in Dec 2010 and Mar 2017. A significant decreasing trend of on-road NO2 was found by comparing the measurements taken in 2010 and 2017. Influences of changes of bus companies operation strategies can also be observed from the measured NO2 concentration maps.
The manuscript presents an investigation of spatio-temporal variability of street level NO2 in...