On the causes of variability in amounts of airborne grass pollen in Melbourne,Australia |
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Authors: | Julian de Morton John Bye Alexandre Pezza Edward Newbigin |
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Institution: | (1) School of Earth Sciences, University of Melbourne, Melbourne, Victoria, 3010, Australia;(2) School of Botany, University of Melbourne, Melbourne, Victoria, 3010, Australia; |
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Abstract: | In Melbourne, Australia, airborne grass pollen is the predominant cause of hay fever (seasonal rhinitis) during late spring
and early summer, with levels of airborne grass pollen also influencing hospital admissions for asthma. In order to improve
predictions of conditions that are potentially hazardous to susceptible individuals, we have sought to better understand the
causes of diurnal, intra-seasonal and inter-seasonal variability of atmospheric grass pollen concentrations (APC) by analysing
grass pollen count data for Melbourne for 16 grass pollen seasons from 1991 to 2008 (except 1994 and 1995). Some of notable
features identified in this analysis were that on days when either extreme (>100 pollen grains m−3) or high (50–100 pollen grains m−3) levels of grass pollen were recorded the winds were of continental origin. In contrast, on days with a low (<20 pollen grains
m-3) concentration of grass pollen, winds were of maritime origin. On extreme and high grass pollen days, a peak in APC occurred
on average around 1730 hours, probably due to a reduction in surface boundary layer turbulence. The sum of daily APC for each
grass pollen season was highly correlated (r = 0.79) with spring rainfall in Melbourne for that year, with about 60% of a declining linear trend across the study period
being attributable to a reduction of meat cattle and sheep (and hence grazing land) in rural areas around Melbourne. Finally,
all of the ten extreme pollen events (3 days or more with APC > 100 pollen grains m−3) during the study period were characterised by an average downward vertical wind anomaly in the surface boundary layer over
Melbourne. Together these findings form a basis for a fine resolution atmospheric general circulation model for grass pollen
in Melbourne’s air that can be used to predict daily (and hourly) APC. This information will be useful to those sectors of
Melbourne’s population that suffer from allergic problems. |
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