UAF Near Real Time MAXDOAS Data Key

	UAF Near Real Time MAXDOAS data key
	The MAXDOAS technique observes the differential slant column density (DSCD), which is the column-integrated abundance of the absorber as a function of observation elevation angle. For a boundary-layer absorber, the highest DSCD values are seen at the lowest elevation angles because these paths have the longest paths through the absorbing boundary layer. The viewing direction switches from northwest to southeast every day at roughly 1:00 UTC in order to avoid direct sunlight. This switching is occasionally evident in the data due to varying conditions in the two directions. These data are presented with the following color scale: Black (20°), Blue (10°), Green (5°), Orange (3°), Red (2°), Purple (1°). Given good visibility, a larger difference between the low elevation data indicates a shallower boundary layer. As a reference point, for clear skies and a well-mixed BrO layer from the surface to 1 km, the 5 degree BrO DSCD is about 50% more than then 10 degree BrO DSCD. Also, for the same 1 km well-mixed boundary layer, 10¹⁴ molecule/cm² DSCD at the 2° elevation angle corresponds to around 5 pptv BrO. Based upon these considerations, we build the following qualitative abundance scale BrO Abundance Scale Low Moderate High We can invert the BrO DSCD versus elevation angle data to a vertical profile of BrO concentration. However, this inversion requires significant time because aerosols and clouds affect the visibility at each elevation angle. We use the oxygen collisional dimer (O₄) DSCD observations to determine atmospheric visibility. The O₄ vertical profile is an exponentially decaying density with a scale height of around 4km, and thus O₄ DSCD values decay less strongly with increasing elevation angles than do BrO, which has a shallower vertical profile. For clear skies and low aerosol scattering, the O₄ DSCD values should be similar between 1 and 5 degree elevations, decreasing slightly at 10 degrees, and then with the 20 degree elevation being about half of the low elevation data. Lower values of O₄ DSCD correspond to diminished visibility (aerosol or clouds). Contacts: Bill Simpson, University of Alaska Fairbanks, ffwrs "at" uaf.edu, 907-474-7235 Dan Carlson, University of Alaska Fairbanks fsdac8 "at" uaf.edu, 907-474-2436 Deanna Donohoue, University of Alaska Fairbanks ddonohoue "at" gi.alaska.edu, 907-474-2436 Return to the data: http://ozone.gi.alaska.edu/maxdoas

UAF Near Real Time MAXDOAS data key

The MAXDOAS technique observes the differential slant column density (DSCD), which is the column-integrated abundance of the absorber as a function of observation elevation angle. For a boundary-layer absorber, the highest DSCD values are seen at the lowest elevation angles because these paths have the longest paths through the absorbing boundary layer. The viewing direction switches from northwest to southeast every day at roughly 1:00 UTC in order to avoid direct sunlight. This switching is occasionally evident in the data due to varying conditions in the two directions.

These data are presented with the following color scale: Black (20°), Blue (10°), Green (5°), Orange (3°), Red (2°), Purple (1°).

Given good visibility, a larger difference between the low elevation data indicates a shallower boundary layer. As a reference point, for clear skies and a well-mixed BrO layer from the surface to 1 km, the 5 degree BrO DSCD is about 50% more than then 10 degree BrO DSCD. Also, for the same 1 km well-mixed boundary layer, 10¹⁴ molecule/cm² DSCD at the 2° elevation angle corresponds to around 5 pptv BrO. Based upon these considerations, we build the following qualitative abundance scale

BrO Abundance Scale
Low
Moderate
High

We can invert the BrO DSCD versus elevation angle data to a vertical profile of BrO concentration. However, this inversion requires significant time because aerosols and clouds affect the visibility at each elevation angle. We use the oxygen collisional dimer (O₄) DSCD observations to determine atmospheric visibility. The O₄ vertical profile is an exponentially decaying density with a scale height of around 4km, and thus O₄ DSCD values decay less strongly with increasing elevation angles than do BrO, which has a shallower vertical profile. For clear skies and low aerosol scattering, the O₄ DSCD values should be similar between 1 and 5 degree elevations, decreasing slightly at 10 degrees, and then with the 20 degree elevation being about half of the low elevation data. Lower values of O₄ DSCD correspond to diminished visibility (aerosol or clouds).

Contacts:

Bill Simpson, University of Alaska Fairbanks, ffwrs "at" uaf.edu, 907-474-7235
Dan Carlson, University of Alaska Fairbanks fsdac8 "at" uaf.edu, 907-474-2436
Deanna Donohoue, University of Alaska Fairbanks ddonohoue "at" gi.alaska.edu, 907-474-2436

Return to the data: http://ozone.gi.alaska.edu/maxdoas