Abstract
Abstract. In this study we present the first long term measurements of atmospheric nitrogen dioxide (NO2) using a LED based Long Path Differential Optical Absorption Spectroscopy (LP-DOAS) instrument. This instrument is measuring continuously in Hong Kong since December 2009, first in a setup with a 550 m absorption path and then with a 3820 m path at about 30 m to 50 m above street level. The instrument is using a high power blue light LED with peak intensity at 450 nm coupled into the telescope using a Y-fibre bundle. The LP-DOAS instrument measures NO2 levels in the Kowloon Tong and Mongkok district of Hong Kong and we compare the measurement results to mixing ratios reported by monitoring stations operated by the Hong Kong Environmental Protection Department in that area. Hourly averages of coinciding measurements are in reasonable agreement (R = 0.74). Furthermore, we used the long-term data set to validate the Ozone Monitoring Instrument (OMI) NO2 data product. Monthly averaged LP-DOAS and OMI measurements correlate well (R = 0.84) when comparing the data for the OMI overpass time. We analyzed weekly patterns in both data sets and found that the LP-DOAS detects a clear weekly cycle with a reduction on weekends during rush hour peaks, whereas OMI is not able to observe this weekly cycle due to its fix overpass time (13:30–14:30 LT – local time).
Highlights
Nitrogen dioxide (NO2) is one of the most important trace gases in the atmosphere with impact on atmospheric chemical processes and public health
The lowest and highest NO2 levels usually occur in the early morning and the evening rush hour, respectively
The annually averaged NO2 mixing ratio measured by the Long Path Differential Optical Absorption Spectroscopy (LP-Differential Optical Absorption Spectroscopy (DOAS)) is about 23.5 ppbv, which is slightly higher than the WHO guideline annual value (21 ppbv), but considerably lower than the Hong Kong air quality annual objective value (42.5 ppbv)
Summary
Nitrogen dioxide (NO2) is one of the most important trace gases in the atmosphere with impact on atmospheric chemical processes and public health. Acid rain caused by NOx is known to have adverse impact on forest, freshwater and soil, harming insects and aquatic life-forms, as well as causing damage to buildings and having a negative impact on public health. NO2 may play an important role in radiative warming of the earth’s atmosphere (Solomon et al, 1999). In Hong Kong, the atmospheric NO2 levels are strongly related to traffic volume (Lau et al, 2008) and power generation. Due to prevailing easterlies in Hong Kong, most of the power plants are built in the western part of Hong Kong to minimize the impact on the populated area. Having an accurate NO2 measurement with high temporal resolution is very important for air quality monitoring and pollution management
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