Manitou Experimental Forest Observatory 	
Trace gas concentrations; Summer, 2015	
John Ortega; National Center for Atmospheric Research	
Atmospheric Chemistry Observations and Modeling.	
	
Trace gas measurements were taken from a common inlet line inside the chemistry trailer to support	
summer 2015 CSU study (PI = D. Farmer).	
Ozone = 2B technologies, model 202	
NO/Nox = Ecophysics Model 88y	
CO = Thermo Model 48C.	
	
From July 9 to August 1, the PTR-MS and trace gasses shared a commone inlet.  A carbon-vane pump pulled air from near the top of the tower	
(27m) into the Chemistry Trailer at 20 L/min (volumetric) using an MKS mass flow controller.	
Some time around July 25, it appears as though there was a leak in the inlet line as well as a flow increase from 20 L/min to 30 L/min.	
On August 1, a new inlet line was established to separate the PTR-MS and the trace gasses.  The new inlet line was ~5 m off the ground	
and controlled to 10 L/min using a critical orifice.	
	
The NOx measurement can only measure NO or NOx at one time.  The NO measurement is chemiluminescence	
of NO reacting with O3.  To measure NOx, the air sample is first directed into a heated Mo cataylyst that converts NO2 into NO 	
keeping existing the NO the same, and then the same NO+O3 reaction is performed.  NO2 is calculated by NO2=NOx-NO.	
	
NO and NOx measurements were switched every 5 minutes.  For the times when NOx was being measured, NO was interpolated between the 5 minute	
periods before and after that measurement.  Similarly, when the NO was being measured, the NOx values were interpolated.	
	
The CO measurement requires a zero reading in order to account for a drifting baseline.  Between 50 minutes after each hour and the	
beginning of each hour (XX:50:00 andXX:50:59), the CO zero measurement was performed.  To calculate the 5 minute averages from 0:00:00 to 0:49:59 of each hour, the 	
background from the adjacent hours were subtracted from the signal and weighted towards the closest hour (e.g. for 20 minutes	
after the hour, 3/5 of the zero value came from the zero of the previous hour, and 2/5 came from the next zero.   The result of that subtraction was multiplied by the calibration coefficient to 	
obtain the CO concentration. 	
	
The CO, O3 and NO measurements were calibrated in the laboratory during May and June 2015 (NCAR FL0 room 3100).  The NO and CO	
measurements were done by diluting ppm-level standards with dry zero air and obtaining a straight line calibration equation of volts vs. ppb.	
The NO calibration was checked against the factory calibration done earlier in the year and was within 5% of that value.	
The ozone calibration was performed by making ozone with a mercury lamp, and diluting with zero air.  The 2B monitor sampled the same	
air stream as a dedicated Thermo O3 monitor (reference standard).  The data collected from both monitors was used to generate the same type of straight line calibration.	
	
All the data was aquired at 10 second intervals.  The data reported here in the various tabs represent 5 minute averages.  Missing data is listed as NaN.	
See column headings for explanations.	
JO;  9/15/2015	