Research News

Pandora Spectrometer Reveals Seasonal Dynamics and Air Quality Insights in Beijing

Jan 31, 2024

A Pandora spectrometer installed on the rooftop of the Aerospace Information Research Institute(AIR)with the Chinese Academy of Sciences (CAS) at its Olympic Park in Beijing has provided valuable insights into the dynamics of nitrogen dioxide (NO2) concentrations over the course of its first year in operation, from August 2021 to July 2022.

NO2, a highly reactive gas with a short atmospheric lifetime of only a few hours, poses a threat to human well-being at high concentrations. The Pandora spectrometer, a high-precision, time-resolved instrument, has been instrumental in monitoring NO2 levels, along with other trace gases such as formaldehyde (HCHO) and ozone (O3).

The study, published in the Atmospheric Measurement Techniques on Jan. 19, reveals intriguing patterns in NO2 concentrations, with elevated levels observed during winter and lower levels in summer. A distinct diurnal cycle is evident, showcasing minimum concentrations during daylight hours. Notably, concentrations witnessed a significant decline during the 2022 Winter Olympics in Beijing, underscoring the efficacy of emission control measures implemented during the event.

Pandora's observations shed light on the impact of wind patterns on air quality in Beijing. Northerly winds bring clean air with low NO2 concentrations, while southerly winds transport pollution from surrounding areas, resulting in higher NO2 levels in the capital. Tropospheric NO2's contribution to the total NO2 VCD exhibits substantial variability on daily and seasonal scales, ranging between 50% and 60% in winter and 60% and 70% in spring and autumn.

A comparison between Pandora-measured surface concentrations and in situ measurements using a Thermo Scientific 42i-TL analyzer reveals intriguing nuances. The data suggests that Pandora concentrations are generally lower, with differing relationships observed at low and high NO2 concentrations. Explanations for these differences are explored in terms of measurement techniques and the influence of physical transport phenomena.

Furthermore, the study leverages Pandora data for the validation of TROPOspheric Monitoring Instrument (TROPOMI) data, indicating that, on average, TROPOMI VCDs are slightly lower but well within the expected error margin. However, the proximity of the Pandora instrument to a sub-orbital TROPOMI pixel introduces a minor error in tropospheric NO2 VCD, emphasizing the need for precise spatial considerations in satellite-based observations.

It is found that the Pandora observations at the Beijing-RADI site are deemed representative of a 10 km radius, providing valuable insights into the broader air quality dynamics in the region.

This research not only underscores the critical role of Pandora spectrometry in understanding urban air quality dynamics but also emphasizes its potential for validating satellite-based observations, contributing to the advancement of atmospheric science.

The Pandora spectrometer installed on the rooftop of AIR's building at its Olympic Park in Beijing. (Image by AIR)