Investigation of winter aerosol dispersion using the MM5/WRF-CAMx4 numerical modelling system: application to the aerosol abatement strategy for the City of Christchurch

摘要

Air circulation and air pollution dispersion models are used by a range of stakeholders involvedin managing air quality in New Zealand following the recent establishment and implementationof the National Environmental (Air Quality) Standards by the Ministry for the Environment.MM5-CAMx4 and WRF-CAMx4 numerical modelling systems were utilized to air circulationover the complex terrain of the Christchurch area for investigation applied to winter aerosolpollution, following the recent establishment and implementation of the National EnvironmentalStandards.A new method using several different chemical scenarios is developed to calculate optimalchemical composition of the input gridded aerosol emissions. This method improves theaccuracy of predicted PM concentrations. The MM5-CAMx4.2 numerical system is evaluated topredict aerosol concentrations over a 48-72 hour time period for Christchurch for winter 2005.The aerosol concentrations are obtained for four different chemical compositions of the inputaerosol emissions. The fine-total PM regression error between observed and modelled aerosol isused to find the minimum difference between modelled and ambient aerosol. Combination of thechemical scenarios with the minimum error between modelled and ambient data is employed tocreate a new complex chemical scenario.A reduction of the systematic error in the scenario method is achieved by applying theMM5/WRF - CAMx4.2 numerical system and observations for winter 2006, aerosol data from 2observation sites. Assessment of the efficiency of PM abatement strategies for the period 2005-2013 is undertaken using winter 2005 meteorology and application of a linear reduction inemissions according to Environment Canterbury proposed plan for aerosol reduction. A newnumerical approach to selection of PM monitoring sites optimal localisation is also developedand could be applied to any air pollutant to find the optimal positions for installing newobservation sites.