3.5. Linearity and detection limit
Peak ozone levels in urban and suburban areas are typically in the
80–150 ppbv range, with higher concentrations only reached in
highly polluted areas that lack controls on emission sources [2]. The
National Ambient Air Quality Standard for ground-level ozone,
established by the US EPA, stipulates a primary ozone standard of
75 ppbv (as a 3-year average of the fourth-highest daily maximum 8-
hour average ozone concentration over a year) [30]. Considering these
values, the behavior of the analytical signal corresponding to different
ozone concentrations in the range 0–150 ppbv was explored under
optimized conditions (using two filters, a sampling flow rate of
0.4 L min−1 and a 15 min sampling time). Three replicates were
measured at each concentration level. Within this concentration
range, the fluorescence intensity of the reaction product increased
linearly with increasing ozone concentration:
S = ð9:58 3:70Þ × 10−2+ ð8:82 0:04Þ × 10−1 O3 ½ R = 0:99995
ð1Þ
where, S represents the fluorescence signal intensity and [O3] the
ozone concentration (in ppbv). The detection limit, calculated as 3
times the standard deviation of the blank signal fluctuation, was 7
ppbv, which is adequate for the measurement of ambient ozone in
urban areas. Lower detection limits could be achieved using longer
sampling times. In highly polluted regions, sampling times shorter
than 15 min and/or sampling flow rates lower than 0.4 L min−1 could
be used.