1 results for Adeeb, Farah

  • A Study of near-surface ozone concentrations in the city of Auckland, New Zealand

    Adeeb, Farah (2006)

    Doctoral thesis
    The University of Auckland Library

    Restricted Item. Print thesis available in the University of Auckland Library or may be available through Interlibrary Loan. This research provides insight into large-scale spatial variation of ozone (O3) distribution in the Auckland region and was designed to increase our understanding of O3 behaviour and distribution in a coastal-urban situation. The research was also carried out with a view to assisting regulatory agencies optimize future monitoring networks, and to help identify locations where human health and natural resources could be at risk in the future. Although the research was limited to one region, the results are valuable for improving the conceptual understanding of formation of high ozone concentrations in a more general sense in the New Zealand and Southern Hemisphere. The work reported in this thesis is aimed at studying O3 concentrations and the influence of the most relevant meteorological variables on an average coastal New Zealand city where precursor emissions are mainly due to traffic exhaust. It deals with the use of Principal Component Analysis method for determining O3 concentrations as a function of meteorological parameters. The study region includes the entire Auckland isthmus, and extends from Whangaparaoa in the North to Pukekohe in the South. Surface O3 data from four sites (Whangaparaoa, Musick Point, the Sky Tower and Pukekohe) for a 4-year period(October 1997 to October 2001) for the Auckland region were examined. Ambient concentration of O3 was characterized in terms of diurnal, weekday/weekend, seasonal and spatial variations in concentration using O3 measurements from the four air quality sites. The monthly average ambient background O3 concentrations at the monitoring sites during this study ranged from 16-30 ppb, much lower than those found in the Northern Hemisphere. The measured seasonal O3 record in the Auckland region, in common with many other remote sites in the Southern Hemisphere, exhibited a summer minimum and a winter maximum. Background concentrations of O3 (as seen in air of marine origin) made a significant contribution to the observed ambient concentrations. A unique feature of Auckland's air quality was the dilution of polluted city air due to the mixing of east coast air into the cleaner west coast circulation leading to overall lower average O3 concentrations in summer. The magnitude, frequency and spatial extent of maximum O3 concentrations were identified, and the observed patterns linked to the prevailing meteorological, topographic, and emission characteristics of the region. However, at no time at any site or season did the O3 concentration exceed the l-hour New Zealand Ministry for the Environment guideline of 75 ppb. O3 depletion was observed to occur at the urban sites, with O3 scavenging by nitric oxide believed to be the dominant depletion mechanism. The seasonal cycle was characterized by elevated O3 concentrations in the winter (nighttime level >24 ppb) and low mixing ratios in the summer (nighttime levels in the range 14-20 ppb). The afternoon O3 maxima found at the three low elevation sites under the impact of "Auckland city" plume were on average, 1.5 to 1.7 times higher than those associated with the "marine sector". A state of the art diagnostic meteorological model, namely CALMET, was used to generate wind fields for the Auckland region. These wind fields were then used to construct backward trajectories on days when high O3 concentrations (episodes up to 6l ppb) were observed. The un-even distribution of the meteorological monitoring sites provided justification for running the diagnostic model CALMET and exploring the utility of using such a model when topography/land use prohibits monitoring sites in certain sections of the domain. It was found that the high O3 events recorded at the monitoring sites during the study period coincided with transport episodes originating from Auckland's urban and industrial areas. For the occurrence of high O3 concentrations at downwind sites, it was found that not only wind direction from the urban areas of Auckland, but that high solar radiation was important as well. On four out of the five cases when photochemical production of O3 was found to occur, high O3 concentrations were associated with a particular type of diurnal evolution of wind direction wind fields associated with the sea breezes. In addition to the analysis of ambient o3 concentrations and O3 episodes, field measurements were carried out in an attempt to detect and subsequently understand the interaction between particulate matter and O3 in the Auckland region, a multivariate statistical analysis approach was utilized. Particulate matter in the size range 2.75-6.25 μm accounted for over 70% of the total aerosol concentration at all sampling sites. Surface area of particulate matter variable (especially in the size class 2.75-4.25 μm) was statistically significant in explaining variation in O3 concentration. However, the net change in the adjusted R2 indicated that the effect of adding particulate matter in the multiple regression model for the present dataset was relatively minor except at Musick Point.

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