Field testing of new-technology ambient air ozone monitors

Figures & data

Table 1. Monitor performance specifications for O₃ based in 40 CFR Part 53

Range	0–0.5 ppm (500 ppb)
Noise	0.005 ppm (5 ppb)
LDL (defined as two times noise)	0.01 ppm (10 ppb)
Interference equivalent each substance	±0.02 ppm (20 ppb)
Interference equivalent total interferences	0.06 ppm (60 ppb)
Zero drift 12 hr	±0.02 ppm (20 ppb)
Zero drift 24 hr	±0.02 ppm (20 ppb)
Span drift 24 hr at 20% of upper range limit	±20.0% (20 ppb)
Span drift 24 hr at 80% of upper range limit	±5.0% (20 ppb)
Lag time	20 min
Rise time	15 min
Fall time	15 min
Precision at 20% of upper range limit	0.01 ppm (10 ppb)
Precision at 80% of upper range limit	0.01 ppm (10 ppb)

Table 2. Variables routinely measured at the Houston site

O3	Wind speed
NO, NOx, NOz	Wind direction
CO	Temperature
SO2	Precipitation
H2S	Solar radiation
Volatile organic compounds (50 PAMS species)	Shelter temperature
PM2.5	Dew point temperature*
Particulate sulfate	Relative humidity*
Particulate carbon
Note: *From Houston Hobby Airport.

Table 3. Specifications of O₃ monitors used in this study

Instrument	Abbreviation	Type	Scrubber	Humidity control	U.S. EPA status
Thermo Scientific model 49C	49C	UV absorption	MnO2	No	FEM
2B Technologies model 211	211	UV absorption	Chemical reaction	Yes	—
Teledyne API model 265E	265E	Chemiluminescence	None required	Yes	FEM

Figure 1. Comparison of rolling 8-hr averages from three O₃ monitors.

Figure 2. Daily maximum 8-hr O₃ average reported by three O₃ monitors relative to three O₃ levels.

Figure 3. Differences in daily maximum 8-hr O₃ average between the new and conventional monitors.

Table 4. Summary of rolling 8-hr O₃ averages during the study (excluding August 26–27)

Parameter	Model 49C	Model 211	Model 265E
Average O3, ppb	22	22	21
Highest O3, ppb	94	93	94
Number of values ≥ 75 ppb	19	16	16
Number of values ≥ 70 ppb	32	29	30
Number of values ≥ 60 ppb	62	56	58
Number of days ≥ 75 ppb	6	4	6
Number of days ≥ 70 ppb	7	7	7
Number of days ≥ 60 ppb	12	10	12

Figure 4. Ranked 8-hr ozone averages for all periods when at least one monitor exceeded 60 ppb (arrows indicate data from August 26–27).

Table 5. Effect of the application of QA/QC results on model 211 rolling 8-hr average O₃ data parameters

Parameter	Raw data	Adjusted for audit results	Adjusted for audit, weekly/monthly calibrations	Adjusted for audit, weekly/monthly calibrations, daily zero/span
Average O3, ppb	25	25	22	21
Highest O3, ppb	94	92	93	94
Number of values ≥ 75 ppb	16	16	16	18
Number of values ≥ 70 ppb	29	29	29	30
Number of values ≥ 60 ppb	64	64	60	59

Figure 5. Difference in daily maximum 8-hour O₃ average between the model 49C and model 211 monitors before and after daily zero/span adjustment.

Figure 6. Difference in daily maximum 8-hr O₃ average between the model 49C and the model 265E monitors before and after daily zero/span adjustment.

Figure 7. Comparison of maximum daily 8-hr O₃ average among three monitors for the four highest O₃ days.

Figure 8. Response of O₃ monitors to VOC mixture containing aromatic hydrocarbons.

Figure 9. Time series of hourly O₃ difference (model 49C minus model 211), sum of aromatic species and nitric oxide for October 16–17.