Multi-Axis Differential Optical Absorption Spectroscopy (CU MAX-DOAS)

The CU MAX-DOAS instrument measures scattered solar light at different elevation angles (0-180˚) above the horizon in order to quantify trace gases in the lower and free troposphere. The state-of-the-art CU MAX-DOAS is designed to have very low residual error in both the ultraviolet and visible spectral ranges, enabling the detection of trace gases (IO, BrO, HCHO, CHOCHO, NO2, O3, SO2, and HONO) in both pristine and polluted environments. Additionally, oxygen collision-induced absorption (O2-O2) is measured as a proxy for aerosol load.

Ground Based MAX-DOAS

The ground-based CU MAX-DOAS (CU GMAX-DOAS) instrument has been deployed at stationary ground sites for time periods ranging from weeks to years, in order to capture temporal trends in trace gases and aerosols. In the past, the CU MAX-DOAS has been deployed at Pensacola, FL (2009-2011); Pasadena and Fontana, CA for CALNEX 2010; Sacramento, CA for CARES 2010; Cape Cod, MA for TCAP 2012; and Storm Peak Laboratory, CO (2021-2023). 

The CU MAX-DOAS is currently deployed at Mauna Loa Observatory, HI (since 2017); Maido Observatory, Réunion Island (since 2017); and the UDAQ Inland Port Site, Salt Lake City, UT (since 2023).

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MAX-DOAS installed on a stationary platform EPA station Pensacola, Florida



The ship-based CU MAX-DOAS (CU SMAX-DOAS) instrument utilizes the MAX-DOAS technique onboard a sea vessel. Due to the constant movement (pitch & roll) of the ship, elevation angle pointing accuracy and stability are important factors in these measurements. The CU SMAX-DOAS telescope is designed to compensate for the ship's motion in real-time. The CU SMAX-DOAS has been deployed at VOCALS 2008, TAO 2009, TAO 2011, and TORERO 2012.

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MAX-DOAS is a multi-platform instrument designed to be installed in a variety of locations. Pictured above is the MAX-DOAS installed on the NOAA R/V Ka'imimoana


Relevant publications:

Evan et al.: Rapid ozone depletion after humidification of the stratosphere by the Hunga Tonga eruption, Science, 382, 6668, doi:10.1126/sciadv.adi5297, 2023.

Koenig et al.: Observed in-plume gaseous elemental mercury depletion suggests significant mercury scavenging by volcanic aerosols, Environ. Sci.: Atmos., doi:10.1039/D3EA00063J, 2023.

Finkenzeller et al.: The gas-phase formation mechanism of iodic acid as an atmospheric aerosol source, Nature Chemistry, 15, 129-135, doi:10.1038/s41557-022-01067-z, 2023.

Verreyken et al.: Characterization of African biomass burning plumes and impacts on the atmospheric composition over the south-west Indian Ocean, Atmos. Chem. Phys., 20, 14821-14845, doi:10.5194/acp-20-14821-2020, 2020.

Wang et al.: Inter-comparison of MAX-DOAS measurements of tropospheric HONO slant column densities and vertical profiles during the CINDI-2 campaign, Atmos. Meas. Tech., 13, 5087-5116, doi:10.5194/amt-13-5087-2020, 2020.

Kreher et al.: Intercomparison of NO2, O4, O3, and HCHO slant column measurements by MAX-DOAS and zenith-sky UV-visible spectrometers during CINDI-2, Atmos. Meas. Tech., 13, 2169-2208, doi:10.5194/amt-13-2169-2020, 2020.

Wang et al.: MAX-DOAS measurements of HONO slant column densities during the MAD-CAT campaign: inter-comparison, sensitivity studies on spectral analysis settings, and error budget, Atmos. Meas. Tech., 10, 3719-3742, doi:10.5194/amt-10-3719-2017, 2017.

Peters et al.: Investigating differences in DOAS retrieval codes using MAD-CAT campaign data, Atmos. Meas. Tech., 10, 955-978, doi:10.5194/amt-10-955-2017, 2017.

Coburn et al.: Mercury oxidation from bromine chemistry in the free troposphere over the southeastern US, Atmos. Chem. Phys., 16, 3743-3760, doi:10.5194/acp-16-3743-2016, 2016.

Volkamer et al.: Aircraft measurements of BrO, IO, glyoxal, NO2, H2O, O2-O2 and aerosol extinction profiles in the tropics: comparison with aircraft-/ship-based in situ and lidar measurements, Atmos. Meas. Tech., 8, 1835-1862, doi:10.5194/amt-8-1835-2015, 2015.

Sinreich et al.: Parameterizing radiative transfer to convert MAX-DOAS dSCDs into near-surface box-averaged mixing ratios, Atmos. Meas. Tech., 6(6), 1521-1532, doi:10.5194/amt-6-1521-2013, 2013.

Coburn et al.: The CU ground MAX-DOAS instrument: characterization of RMS noise limitations and first measurements near Pensacola, FL of BrO, IO, and CHOCHO, Atmos. Meas. Tech., 4, 2421-2439, doi:10.5194/amt-4-2421-2011, 2011

Sinreich et al.: Ship-based detection of glyoxal over the remote tropical Pacific Ocean, Atmos. Chem. Phys., 10(23), 11359-11371, doi:10.5194/acp-10-11359-2010, 2010.

Sinreich et al.: MAX-DOAS detection of glyoxal during ICARTT 2004, Atmos. Chem. Phys., 7(5), 1293-1303, doi:10.5194/acp-7-1293-2007, 2007.