Title : Investigating the Influence of Synoptic - Scale 1 Meteorology on Air Quality Using Self - Organizing Maps and 2 Generalized Additive Modelling

29 The influence of synoptic-scale circulations on air quality is an area of increasing interest to 30 air quality management in regards to future climate change. This study presents an analysis 31 where the dominant synoptic " types " over the region of Melbourne, Australia are determined 32 and linked to regional air quality. First, a self-organising map (SOM) is used to generate a 33 time series of synoptic charts that classify the annual daily circulation affecting Melbourne 34 into 20 different synoptic types. SOM results are then employed within the framework of a 35 generalized additive model (GAM) to identify links between synoptic-scale circulations and 36 observed changes air pollutant concentrations. The GAMs estimate shifts in pollutant 37 concentrations under each synoptic type after controlling for long-term trends, seasonality, 38 weekly emissions, spatial variation, and temporal persistence. Results showed the aggregate 39 impact of synoptic circulations in the models to be quite modest as only 5.1% of the daily 40 variance in O 3 , 4.7% in PM 10 , and 7.1% in NO 2 were explained by shifts in synoptic 41 circulations. Further analysis of the partial residual plots identified that despite a modest 42 response at the aggregate level, individual synoptic categories had differential effects on air 43 pollutants. In particular, increases of up to 40% in NO 2 and PM 10 and 30% in O 3 occur when 44 a synoptic conditions result in a north-easterly gradient wind over the Melbourne area. 45 Additionally, NO 2 and PM 10 levels also showed increases of up to 40% when a strong high 46 pressure system was centered directly over the Melbourne area. In sum, the unified approach 47 of SOM and GAM proved to be a complementary suite of tools capable of identifying the 48 entire range synoptic circulation patterns over a particular region and quantifying how they 49 influence local air quality.