Differential Optical Absorption Spectroscopy in Atmospheric Monitoring

Differential Optical Absorption Spectroscopy (DOAS) is a powerful remote-sensing method that exploits the distinctive, narrow-band absorption structures of atmospheric trace gases in the ultraviolet and visible spectral regions. By analysing the differential absorption of scattered sunlight, DOAS instruments can quantify concentrations of ozone, nitrogen dioxide, formaldehyde and other key species. A multi-axis configuration (MAX-DOAS) extends this approach by recording spectra at different elevation angles, enabling the retrieval of vertical concentration profiles and column densities. Together with advanced radiative transfer and inversion algorithms, MAX-DOAS provides high temporal resolution observations of pollutant layering, boundary-layer dynamics and long-range transport. Recent efforts have refined reference spectra selection, optimised a priori profile constraints and fused multi-platform measurements to close sensitivity gaps in the near surface and free troposphere. The technique underpins global air-quality monitoring, supports satellite validation and informs emission-control strategies by delivering spatially and vertically resolved data on reactive gases and aerosols.

Research from Nature Portfolio

Recent studies have demonstrated the capability of spectroscopic profiling to quantify rapid changes in urban air quality during intensive emission-control campaigns. Analyses of event-driven interventions revealed abrupt NO₂ column declines of up to 40 %, attributable to local measures and shifts in regional transport patterns. Complementary observations of formaldehyde-to-NO₂ ratios provided insights into altered ozone formation regimes, confirming that reductions in NO₂ can suppress or enhance ozone production depending on the prevailing photochemical environment. Such findings underscore the dual role of local emission reductions and meteorological influences in modulating reactive gas distributions.

Differential Optical Absorption Spectroscopy in Atmospheric Monitoring publication trend

The graph below shows the total number of articles in differential optical absorption spectroscopy in atmospheric monitoring across all publications each year (not limited to Nature Index journals).

Technical terms

Differential Optical Absorption Spectroscopy (DOAS): A remote-sensing technique that quantifies trace gases by analysing their characteristic wavelength-dependent absorption features in scattered sunlight.

Multi-Axis DOAS (MAX-DOAS): An extension of DOAS using multiple viewing angles to retrieve vertical profiles and column densities of atmospheric constituents.

Vertical Column Density (VCD): The integrated concentration of a trace gas throughout a vertical column of the atmosphere, typically expressed in molecules cm⁻².

Aerosol Optical Depth (AOD): A measure of light extinction by aerosols across the entire atmospheric column, indicating the total particle load.

A priori profile: An initial estimate of a species’ vertical distribution used as a constraint in profile retrieval algorithms to stabilise inversion results.

References

1. Ozone profiles without blind area retrieved from MAX-DOAS measurements and comprehensive validation with multi-platform observations. Remote Sensing of Environment (2023).
2. Vertical profiles of NO2, SO2, HONO, HCHO, CHOCHO and aerosols derived from MAX-DOAS measurements at a rural site in the central western North China Plain and their relation to emission sources and effects of regional transport. Atmospheric Chemistry and Physics (2019).
3. A Novel Hyperspectral Remote Sensing Technique with Hour-Hectometer Level Horizontal Distribution of Trace Gases: To Accurately Identify Emission Sources. Journal of Remote Sensing (2023).