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Title: Trace-Gas Mixing in Isolated Urban Boundary Layers: Results from the 2001 Phoenix Sunrise Experiment

Abstract

Measurements made from surface sites, from the 50-m and 140-m levels (the 16th and 39th floors) of a skyscraper and from an instrumented aircraft are used to characterize early morning profiles of CO, NOy and O3 within the mid-morning summertime convective atmospheric boundary layer (CABL) over Phoenix, Arizona. Although mixing was anticipated to produce uniform values of these species throughout the CABL, this was found not to be the case. Background air advected into the upper levels of the boundary layer and entrained air from above appears to be the most likely cause for the lack of well-mixed trace gases. The results show that surface measurements may provide only limited information on concentrations of trace gas species higher in the boundary layer.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
876837
Report Number(s):
PNNL-SA-45339
Journal ID: ISSN 0004-6981; ATENBP; KP1202010; TRN: US200608%%304
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Atmospheric Environment; Journal Volume: 40; Journal Issue: 1
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; BOUNDARY LAYERS; GASES; AIR POLLUTION; OZONE; air pollution; CO; Ozone; Noy; mixing; convective atmospheric boundary layer

Citation Formats

Berkowitz, Carl M., Doran, J C., Shaw, William J., Springston, Stephen R., and Spicer, Chet W. Trace-Gas Mixing in Isolated Urban Boundary Layers: Results from the 2001 Phoenix Sunrise Experiment. United States: N. p., 2006. Web. doi:10.1016/j.atmosenv.2005.08.039.
Berkowitz, Carl M., Doran, J C., Shaw, William J., Springston, Stephen R., & Spicer, Chet W. Trace-Gas Mixing in Isolated Urban Boundary Layers: Results from the 2001 Phoenix Sunrise Experiment. United States. doi:10.1016/j.atmosenv.2005.08.039.
Berkowitz, Carl M., Doran, J C., Shaw, William J., Springston, Stephen R., and Spicer, Chet W. Sun . "Trace-Gas Mixing in Isolated Urban Boundary Layers: Results from the 2001 Phoenix Sunrise Experiment". United States. doi:10.1016/j.atmosenv.2005.08.039.
@article{osti_876837,
title = {Trace-Gas Mixing in Isolated Urban Boundary Layers: Results from the 2001 Phoenix Sunrise Experiment},
author = {Berkowitz, Carl M. and Doran, J C. and Shaw, William J. and Springston, Stephen R. and Spicer, Chet W.},
abstractNote = {Measurements made from surface sites, from the 50-m and 140-m levels (the 16th and 39th floors) of a skyscraper and from an instrumented aircraft are used to characterize early morning profiles of CO, NOy and O3 within the mid-morning summertime convective atmospheric boundary layer (CABL) over Phoenix, Arizona. Although mixing was anticipated to produce uniform values of these species throughout the CABL, this was found not to be the case. Background air advected into the upper levels of the boundary layer and entrained air from above appears to be the most likely cause for the lack of well-mixed trace gases. The results show that surface measurements may provide only limited information on concentrations of trace gas species higher in the boundary layer.},
doi = {10.1016/j.atmosenv.2005.08.039},
journal = {Atmospheric Environment},
number = 1,
volume = 40,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • A field experiment was carried out in Phoenix during June 2001 to examine the role of vertical mixing on the ozone chemistry of the boundary layer during the morning transition from stable to unstable atmospheric conditions. A combination of surface instruments, instruments located on two floors of a 39-story building in downtown Phoenix, and an instrumented airplane was used to characterize the evolving chemistry in the lowest 650 m of the atmosphere. Remote sensing and in situ platforms were used to obtained detailed profiles of winds and temperatures during the early morning hours and for several hours after sunrise. Themore » analysis presented in this paper focuses on vertical profiles of CO, ozone, and NO/NOy measured on the building and their relationship to the morning boundary layer evolution over Phoenix. Some features were found that are consistent with a simple conceptual picture of nighttime trapping of pollutants in a stable surface layer and a subsequent release the following morning. In some instances, however, evidence of significant vertical mixing was found during the early morning well before the times expected for the development of convective mixing after sunrise. A satisfactory explanation for these observations has not yet been found.« less
  • The role of boundary layer mixing is increasingly recognized as an important factor in determining the concentrations of ozone and other trace gases near the surface. While the concentrations at the surface can vary widely due to horizontal transport of chemical plumes, the boundary layer is also characterized by turbulence that follows a diurnal cycle in height and intensity. Surface oxidant concentrations can therefore undergo significant changes even in the absence of photochemistry. A central goal of the Phoenix 2001 Field Campaign was to study vertical mixing with the onset of convection and to quantify the effect of this mixingmore » on chemistry within an urban boundary layer. As part of this study, a series of low altitude aircraft sampling flights were made over the Greater Phoenix area between June 16-30, 2001. The resulting observations, in conjunction with a series of surface measurements and meteorological observations, are being used to study the vertical transport and reactivity of ozone and ozone-precursors shortly after sunrise. Additional details of this campaign are given in Doran, et al. (2002). It was anticipated that turbulence over Phoenix at night would be suppressed as a result of cooling of the boundary layer over the city. By sampling shortly after sunrise, we hoped to collect measurements above the residual nocturnal stable layer and to continue sampling through the developmental period of a convectively active boundary layer. We report here on the first analysis of these observations, made from a Gulstream-1 (G-1) aircraft operated by the U.S. Department of Energy.« less
  • A central goal of the Phoenix 2001 Field Campaign was to study vertical mixing with the onset of convection and to quantify the effect of this mixing on chemistry within an urban boundary layer. As part of this study, a series of low altitude aircraft sampling flights were made over the Greater Phoenix area between June 16-30, 2001. The resulting observations, in conjunction with a series of surface measurements and meteorological observations, are being used to study the vertical transport and reactivity of ozone and ozone-precursors shortly after sunrise. A typical flight began with sampling in the residual boundary layermore » of the preceding afternoon, showing a large vertical gradient in both chemical and meteorological species. With the development of the convective boundary layer, these gradients disappeared, and a more uniform value was found at all altitudes in the more slowly reacting species. Ozone levels were typically observed to be greatest aloft during the early morning hour s, with values typically twice those found near the surfaces. NOy was inversely related to ozone at the start of the flights, as would be expected from the O3+ NO reaction, suggesting the upward mixing of NOx rich air with the downward transport of NOx-poor, O3 rich air. The timing of the development of the convective boundary layer, as measured by the weakening of chemical stratification, appeared to be related to the intensity of the residual nocturnal stable layer.« less
  • We report here on combined meteorological and chemical trace-gas observations made from two levels of a skyscraper in downtown Phoenix, Arizona. These observations were made as part the U.S. Department of Energy's Phoenix Sunrise Campaign in June 2001. The motivation for this campaign developed from studies in other urban areas that found peak ozone values above the surface layer appeared to play an important role in governing the surface ozone concentrations in the early morning. The first examination of the data here suggests (a) the vertical extent of the boundary layer before sunrise is below 200 m and the concentrationsmore » of trace gases are very sensitive to the stability of the atmosphere, as shown by the observed gradients. Capturing these processes with an air quality model will require a very high degree of vertical resolution. (b) Typically at night, and sometimes during the day, we would see lower concentrations of ozone at the ground, as expected from the titration of O3 with N O. On June 26 this difference throughout much of the day was of order 10 to 15 ppb. It is not clear if this is a local effect associated with street canyons, or representative of what actually occurs over the entire city and environs. (c) DOAS observations highlight the relationship between the gradient structure of reactive trace gases and meteorology at night.« less
  • The use of an airship as a platform to conduct atmospheric chemistry, aerosol, and cloud microphysical research is described, and results from demonstration flights made off the Oregon coast are presented. The slow speed of the airship makes it an ideal platform to do high-spatial resolution profiling both vertically and horizontally, and to measure large aerosol and cloud droplet distributions without the difficulties caused by high-speed aircraft sampling. A unique set of data obtained during the demonstration flights show the effect that processing marine boundary layer aerosol through stratus clouds has on the aerosol size distribution. Evidence of new particlemore » formation (nucleation of particles) was also observed on about half the days on which flights were made. 11 refs., 9 figs., 1 tab.« less