INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 34: 1883–1897 (2014) Published online 14 August 2013 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/joc.3808 Effects of local, synoptic and large-scale climate conditions on daily nitrogen dioxide concentrations in Auckland, New Zealand Ningbo Jiang, a * Kim N. Dirks b and Kehui Luo c a Office of Environment and Heritage, NSW Department of Premier and Cabinet, Sydney, Australia b School of Population Health, The University of Auckland, New Zealand c Department of Statistics, Macquarie University, Sydney, Australia ABSTRACT: As with many urban centres around the world, nitrogen dioxide (NO 2 ) is of concern in Auckland, New Zealand because of its possible link to respiratory and heart disease. It has also been associated with the frequent occurrence of brown haze in the region. This article examines quantitatively the differential effects of the local-, synoptic- and large-scale (El Ni˜ no-Southern Oscillation – ENSO, Southern Annular Mode – SAM) climate conditions on daily NO 2 concentrations in urban Auckland under the framework of generalized linear models. The local meteorology is found to be the most important driver of the daily NO 2 concentrations in Auckland, primarily through the coupling of local-scale atmospheric flow and stability conditions with local emissions and chemical processes. Both the synoptic circulation and large-scale climate modes play significant roles in determining the local air pollution. Synoptic circulations, even after controlling for the local meteorological conditions, modulate the daily NO 2 at a regional level via two main mechanisms: (1) blocking types facilitate the transport of clean oceanic air over the Auckland landmass, leading to generally low NO 2 concentrations; (2) westerly cyclonic types contribute to region-wide increases in NO 2 concentrations due to the enhanced mixing-in and/or downward transport of ozone (O 3 ) from the upper troposphere or stratosphere. The large-scale climate modes, ENSO and SAM, modulate the regional air quality through changing the frequency of occurrence and air-mass characteristics of synoptic systems over New Zealand. Overall, this study demonstrates a holistic approach to understand how atmospheric circulations of different scales affect local air quality and thus provides useful information for the formulation of effective public health management and planning strategies in response to future climate variability and change. KEY WORDS air quality; local meteorology; synoptic circulation; ENSO; SAM; generalized linear model; self-organizing map; public health management Received 4 April 2013; Revised 6 July 2013; Accepted 25 July 2013 1. Introduction New Zealand’s weather and climate are influenced by a range of atmospheric circulation features (Jiang et al., 2012a, 2012b). The prevailing winds are westerly and south-westerly, but north-easterly flows are also signifi- cant (Hessell, 1988). Local weather patterns are primarily determined by interactions between the local terrain (and associated local circulation features such as land–sea breezes) and synoptic circulations, which are character- ized by eastward-migrating anticyclones/ridges, depres- sions/troughs and frontal systems over New Zealand. Large-scale climate modes, in particular the El Ni˜ no- Southern Oscillation (ENSO) and the Southern Annular Mode (SAM), are also known to have significant influ- ence on New Zealand’s climate variability (Salinger and * Correspondence to: N. Jiang, Climate and Atmospheric Science Branch, Office of Environment and Heritage, New South Wales Department of Premier and Cabinet, PO Box 29, Lidcombe, NSW 1825, Australia. E-mail: ningbo.jiang@environment.nsw.gov.au Mullan, 1999; Salinger et al., 2001; Jiang et al., 2004; Kidston et al., 2009). These circulation features, as well as other earth-atmospheric processes, interact with each other both in time and space (Sturman and Tapper, 2008), leading to the observed complex climatic conditions at specific locations, such as Auckland. Auckland is the largest city in New Zealand, having one third of the country’s population. Its metropolitan area is situated on a narrow isthmus (Figure 1), character- ized by a high population density, several large industrial areas and high traffic volumes. Air contaminants emitted from the urban area have a potential to impact on the entire regional airshed (ARC, 1997; Covec, 2005). Road traffic is the most significant anthropogenic source of the air pollutants emitted into the urban airshed, accounting for about 90% of NO x (NO 2 and NO), 86% of CO, 77% of SO 2 , 59% of volatile organic compounds (VOCs) and 51% of PM 10 emissions within urban Auckland (ARC, 2006a). In general, Auckland’s maritime environment, with its isthmus geography, typically ensures relatively high wind speeds and thus good air quality compared  2013 Royal Meteorological Society