Spatiotemporal inhomogeneity in NO
2
over Fukuoka observed by
ground-based MAX-DOAS
Hisahiro Takashima
a, b, *
, Yugo Kanaya
b
, Hitoshi Irie
c
a
Faculty of Science, Fukuoka University, Fukuoka, Japan
b
Department of Environmental Geochemical Cycle Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan
c
Center for Environmental Remote Sensing (CEReS), Chiba University, Chiba, Japan
highlights
NO
2
profile observations have been made by using MAX-DOAS at Fukuoka, an urban area.
NO
2
inhomogeneity is strongly related to transport associated with a landesea breeze.
Observation by MAX-DOAS is a powerful tool for understanding of pollutant transport.
article info
Article history:
Received 23 February 2014
Received in revised form
24 October 2014
Accepted 31 October 2014
Available online 31 October 2014
Keywords:
Nitrogen dioxide
MAX-DOAS
Boundary layer
Land-sea breeze
Japan
abstract
Continuous NO
2
profile observations have been made using ground-based Multi-Axis Differential Optical
Absorption Spectroscopy (MAX-DOAS) at Fukuoka (33.55
N, 130.36
E), an urban area in Japan.
Throughout the year, NO
2
variations measured by MAX-DOAS (0e100 m) are in good agreement with in
situ surface NO
2
measurements on several-day, week-to-week, and seasonal timescales. We investigated
the spatiotemporal inhomogeneity in NO
2
over Fukuoka by observing at two azimuth angles: the Tenjin
(towards the city center) and Itoshima (away from the city center) directions. In terms of diurnal vari-
ations, NO
2
in both directions show clear morning maxima, on account of local emissions in the morning
and the development of a boundary layer. The concentrations in the early morning are nearly the same in
both directions, but they are higher in the Tenjin direction during most of the daytime on average.
Variability in both directions, as well as spatial inhomogeneity, is large during most of the daytime except
for in the morning. The diurnal maximum for 0e1 km between 10 and 13 LT is sometimes observed in
the Tenjin direction; in some cases, 1 h after this maximum, a maximum is also observed in the Itoshima
direction. The NO
2
maxima for the upper level (1e2 km) in both directions are also delayed from the
maximum in the Tenjin direction for 0e1 km. Analysis of the surface wind field indicates that the NO
2
inhomogeneity is strongly related to vertical/horizontal transport of high concentrations of NO
2
from the
city center, and to horizontal transport of low concentrations from the ocean via a landesea breeze.
Three-dimensional continuous observations by MAX-DOAS are potentially a powerful tool for increasing
our understanding of pollutant transport and mixing in urban areas.
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
Satellite observations have revealed monotone increasing con-
centrations of tropospheric nitrogen dioxide (NO
2
) over the Asian
continent, including China, in recent decades, due to increases in
anthropogenic emissions (e.g., Richter et al., 2005; Irie et al., 2009;
Ma et al., 2013). Among these emissions, NO
2
is one of the most
important species for tropospheric chemistry, including ozone
chemistry, and is therefore important for understanding our at-
mospheric environment. The main sources of nitrogen oxides
(NO
x
¼ NO
2
þ NO) are fossil fuel combustion, biomass burning, and
production from natural sources (soil and lightning). In urban areas,
the main source is fossil fuel combustion, and spatial variations in
NO
x
concentrations are large on account of the spatial complexity of
emission sources and the short photochemical lifetimes of NO
x
species. To enhance our knowledge of tropospheric chemistry, it is
important to gain a quantitative understanding of the impact of the
emission changes on the chemical balance over both the source
area and the surrounding area. * Corresponding author. Faculty of Science, Fukuoka University, Fukuoka, Japan.
E-mail address: hisahiro@fukuoka-u.ac.jp (H. Takashima).
Contents lists available at ScienceDirect
Atmospheric Environment
journal homepage: www.elsevier.com/locate/atmosenv
http://dx.doi.org/10.1016/j.atmosenv.2014.10.057
1352-2310/© 2014 Elsevier Ltd. All rights reserved.
Atmospheric Environment 100 (2015) 117e123