Effect of cloud-to-ground lightning and meteorological conditions on surface NOx and O₃ in Hong Kong

Abstract

Cloud-to-ground (CG) lightning, meteorological conditions and corresponding surface nitrogen oxides (NOx) and ozone (O₃) variations in relation to thunderstorm and lightning activities over Hong Kong at Kwai Chung (urban), Tung Chung (new town) and Tap Mun (background) during active lightning seasons from 2009 to 2013 were studied by analyzing respective air quality monitoring station data along with CG lightning and meteorological data. We observed NOx enhancement and significant O₃ decline on lightning days. Influences of land use types, lightning activities and meteorological conditions on surface NOx and O₃ were examined. NOx and O₃ concentrations shifted towards higher and lower levels, respectively, during lightning days especially in the dominant wind directions. Principal component analysis/absolute principal component scores (PCA/APCS) method and stepwise multiple linear regression (MLR) analysis were employed to examine the influence of thunderstorm related lightning and meteorological parameters on surface NOx and O₃. Wind speed was supposed to be the most important meteorological parameter affecting the concentration of NOx, and lightning activities were observed to make a positive contribution to NOx. Negative contribution of hot, cloudy and wet weather and positive contribution of wind speed were found to affect the concentration of O₃. Lightning parameters were also found to make a small positive contribution to O₃ concentration at Tap Mun and Tung Chung, but the net effect of lightning activities and corresponding meteorological conditions was the decrease of O₃ on lightning days. Reasonably good agreement between the predicted and observed NOx and O₃ values indicates that PCA/APCS-MLR is a valuable method to study the thunderstorm induced NOx and O₃ variations.