Atmospheric nitrogen dioxide measurements in Hong Kong using long path differential optical absorption spectroscopy

Abstract

Long term measurements of atmospheric nitrogen dioxide (NO2) are performed using a Fibre Long Path Differential Optical Absorption Spectroscopy (LP-DOAS) instrument since December 2009 in Hong Kong. The instrument is using a high power blue LED with peak intensity at 450 nm as the light source to sample a path about 30 m to 50 m above the street level. Two setups with total absorption paths of 550 m and 3820 m are used in this study. The measurements are used to give better insights in surface air pollution conditions in Hong Kong. This thesis presents a detailed description of the instrument setup and the automated data retrieval. The LP-DOAS measurements were performed in Kowloon Tong and Mong Kok district in Hong Kong. The measurement results are compared to the concentration from a nearby monitoring station, operated by the Hong Kong Environmental Protection Department. Hourly averages of coinciding measurements are in reasonable agreement (R=0.73 on average). Additionally, NO2 coinciding measurements using the Ozone Monitoring Instrument (OMI) are compared to the LP-DOAS data. Monthly averaged LP-DOAS and OMI measurements correlate well (R=0.77). The comparison of mean weekly cycle however, displays different characteristics. The daily and weekly cycles of NO2 measured by the LP-DOAS are used to indentify different sources of NO2 in Hong Kong.