Abstract:
On occasional winter mornings, a brown haze is visible over Auckland. For a country which markets itself abroad as being clean and green, the sight of a brown cloud hanging over its largest city can be costly to New Zealand. Yet little is known about the conditions under which such haze events form, nor the composition of the haze. This thesis consists of two components addressing each of these using a 10-year series of digital photographs of Auckland’s skyline, surface meteorological measurements, and a one-season field campaign attempting to identify the composition of the brown haze on days when a haze was observed. Digital photographs were analysed and incidences of brown haze were ranked according to severity over a period of 10 years from May 2001 through until August 2011. Using these photographs, 88 brown haze events were identified. Of these, 43 were classed as severe events and 45 as moderate events. These events were then subjugated into groupings according to Kidson type synoptic weather influences over Auckland from midnight to midday of the day in which the haze event occurred. Results from this analysis indicate that two Kidson synoptic weather types H and HSE were are dominant for 74% of the time when brown haze occurs over Auckland. Ground based meteorological data was then used to define conditions during winter mornings when brown haze occurred. This revealed that the intensity of the haze events increases as the wind speed and temperature decrease and the relative humidity increases. Such cold, calm and humid conditions are those typically associated with the H and HSE Kidson weather types. A field campaign was carried out from June – August 2011 to investigate the relationship between particulate concentration at rooftop level and the occurrence of brown haze and to ascertain the vertical concentration of Nitrogen Dioxide (NO2) in the urban atmosphere on these days. To attain this, a multi-channeled particle counter and a Multi-Axis Differential Optical Absorption Spectrometer (MAX DOAS) were installed at a central Auckland location away from direct emission sources. The results from the field campaign indicate that particulate concentration in the accumulation mode size range seems to be more closely linked to haze formation than NO2 detected through the atmosphere by the MAX DOAS. However, raised NO2 levels from ground level instruments indicate the presence a strong ground based inversions under these conditions.