Characterizing the impacts of vertical transport and photochemical
ozone production on an exceedance area
Emma L. Yates
a, *
, Laura T. Iraci
a
, David Austerberry
a, 1
, R. Bradley Pierce
b
,
Matthew C. Roby
a, c
, Jovan M. Tadi
c
a, 2
, Max Loewenstein
a
, Warren Gore
a
a
Atmospheric Science Branch, NASA Ames Research Center, Moffett Field, CA 94035, USA
b
NOAA/NESDIS Advanced Satellite Products Branch Madison, WI 53706, USA
c
Department of Meteorology, San Jose State University, San Jose, CA 95192-0104, USA
highlights
Observation-based analysis of ozone (O
3
) in California and consequences for air quality policy.
Assessment of the seasonality of O
3
production above California's San Joaquin Valley.
Evidence that free tropospheric air affects ground-level O
3
.
Insights into O
3
transport which is difficult to identify by traditional modeling-based approach.
article info
Article history:
Received 13 March 2014
Received in revised form
28 August 2014
Accepted 1 September 2014
Available online 2 September 2014
Keywords:
Tropospheric ozone
Air quality
San Joaquin Valley
abstract
Offshore and inland vertical profiles of ozone (O
3
) were measured from an aircraft during 16 flights from
January 2012 to January 2013 over the northern San Joaquin Valley (SJV) and over the Pacific Ocean.
Analysis of in situ measurements presents an assessment of the seasonality and magnitude of net O
3
production and transport within the lower troposphere above the SJV. During the high O
3
season (May
eOctober), the Dobson Unit sum of O
3
in the 0e2 km above sea level (km.a.s.l.) layer above the SJV
exceeds that above the offshore profile by up to 20.5%, implying net O
3
production over the SJV or vertical
transport from above. During extreme events (e.g. Stratosphere-to-troposphere transport) vertical fea-
tures (areas of enhanced or depleted O
3
or water vapor) are observed in the offshore and SJV profiles at
different altitudes, demonstrating the scale of vertical mixing during transport. Correlation analysis
between offshore O
3
profiles and O
3
surface sites in the SJV lends further support the hypothesis of
vertical mixing. Correlation analysis indicates that O
3
mixing ratios at surface sites in the northern and
middle SJV show significant correlations to the 1.5e2 km.a.s.l. offshore altitude range. Southern SJV O
3
surface sites show a shift towards maximum correlations at increased time-offsets, and O
3
surface sites at
elevated altitudes show significant correlations with higher offshore altitudes (2.5e4 km.a.s.l.).
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
The United States Environmental Protection Agency (EPA) sets
National Ambient Air Quality Standards (NAAQS) for ground-level
ozone (O
3
). The 2008 NAAQS for O
3
requires that the 3-year
average of the annual 4th-highest daily maximum 8-h mean
mixing ratio be less than or equal to 75 parts per billion by volume
(ppb) (US EPA, 2006). The California Air Resources Board (CARB)
sets more stringent 1-h and 8-h O
3
standards at 90 ppb and 70 ppb
respectively to better address longstanding O
3
problems (CARB,
2005). The formulation of attainable O
3
standards relies on the
accurate identification of a representative baseline mixing ratio of
O
3
that would occur in the United States in the absence of recent,
locally emitted or produced anthropogenic pollution, as defined by
the Task Force on Hemispheric Transport of Air Pollution (Dentener
et al., 2011). Current baseline O
3
mixing ratios are estimated to be in
the range of 15e60 ppb, with estimates varying based on model
and experimental uncertainties, season, location and elevation
(Fiore et al., 2003; Lefohn et al., 2011; Zhanget al., 2011; Lin et al.,
* Corresponding author.
E-mail address: emma.l.yates@nasa.gov (E.L. Yates).
1
Now at: Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann
Arbor, MI 48109-2143, USA.
2
Now at: Department of Global Ecology, Carnegie Institution for Science, Stan-
ford, CA 94305, USA.
Contents lists available at ScienceDirect
Atmospheric Environment
journal homepage: www.elsevier.com/locate/atmosenv
http://dx.doi.org/10.1016/j.atmosenv.2014.09.002
1352-2310/© 2014 Elsevier Ltd. All rights reserved.
Atmospheric Environment 109 (2015) 342e350