North Atlantic Oscillation and its Influence on Ozone in London

North Atlantic Oscillation

NAO Index Magnitude of a NAO event is categorized by and index value The amplitude is determined such that the combined sum of the products with the corresponding pattern eigenvectors explains the maximum spatial structure of the observed height anomaly field during the month. The amplitudes were then assembled into a continuous time series, and standardized. Translation: The CPC takes geopotential height anomalies, averages them and assigns a value based on variation in height between two locations

Is NAO Important?

Hypothesis The positive phase of the NAO brings stronger advection of polluted air from North America Combined with local sources, during NAO + concentrations of Ozone should be higher in London During NAO – phase concentrations of Ozone should be lower due to the loss of inter-hemispheric transport from North America

Calculations Statistical Analysis of Ozone concentration deviations from average at London – Bloomsbury station (5-10 km NW of downtown) near the British Museum. Correlation Analysis between NAO Index Value and Deviation

Results Correlation O3 Dev and NAO Index 0.33 Correlation O3 Dev and NAO + Events 0.22 Correlation O3 Dev and NAO - Events 0.06 With a significance level of α = .01, the calculated correlation coefficients for row 1 and 2 are greater than the critical value and are hence significant NAO (-) phase correlation fall short

Conclusions Correlation between O3 concentrations and NAO Index is present however only strong correlation is with NAO positive events Strong advection into British Isles most likely brings polluted air from the North American coast during NAO positive phase NAO negative phase demonstrates lower O3 concentrations, however more stagnant air may allow for local sources of O3 to build up Variations in meteorology may be the cause for many of the deviations from expected correlation

Trouble Brewing? Trend of increasing values of NAO index What will this suggest for future air quality in the British Isles?