Central California Ozone Study (CCOS) - Desert Research Institute

(e.g., HNO 3 , PAN, N 2 O 5 , HONO, and NO 3 ). Therefore the thermal catalytic method is used to
measure NO, and then NO plus other nitrogen oxides as a group. If the group is not well defined, it
is referred commonly as NO x , since the species included in the group depend on factors such as
inlet and line losses and environmental factors. HNO 3 is most prone to line losses. Placing the
converter as close to the sample inlet as possible minimizes these losses. Chemiluminescence
analyzers that are configured in this manner are commonly known as NOy analyzers. NOy, or
reactive nitrogen oxides, consists of a variety of species, the most abundant of which are NO,
NO2, PAN and HNO 3 . TEI Model 42CY is configured with dual converters, which allows
estimates of HNO3 by difference between the signals with and without an in-line nylon filter or
NaCl impregnated fiber denuder.
C.4 Supplemental Measurements of Ozone
Supplemental air quality measurements are needed during intensive operational periods
(IOPs) in order to examine the three-dimensional distribution of ozone in the study area and to
quantify some of the important species, other than those routinely monitored, which participate in
ozone photochemistry.
C.4.1 Ozonesondes
In addition to atmospheric pressure, temperature, and moisture (relative humidity or wet
bulb temperature), balloon-borne radiosondes can be equipped with instrumentation to measure the
vertical distributions of ozone mixing ratios. Ozonesondes have lower quantifiable limit of less
than 15 ppb with precision of ± 5 ppb or ± 10%.
Ozonesondes provide ozone data that are averaged over short vertical distances and are
thus nearly instantaneous measurements at a particular location. The data are only "snapshots" at
each level of the atmosphere. As the radiosonde rises, it can be transported downwind, so
measurements are not made above a fixed location. The typical response time of the instrument (>
80% of step change in 1 minute) may affect accuracy during ascent through sharp gradients in
ozone mixing ratios. Balloon soundings usually can be made two to eight times per day on
selected sampling days within reasonable budget contraints, but they are not cost-effective for
long-term monitoring. Use of ozonesondes are most cost-effective when coupled to existing
radiosonde releases.
C.4.2 Ozone Aloft
Lidar Measurements
The Elight Ozone Profiler measure vertical ozone profiles starting at approx. 50 m up to
2000 m with a detection limit of 1mg/m³ * m. This corresponds to a detection limit of 5µg/m³ with
200 m range resolution. The system can be delivered as outdoor version with air-water cooling
and with water-water cooling as indoor version. The optics and the electronics are integrated in an
outdoors housing which allows system operation under different weather conditions. In the system
a data analysis software package is implemented for the on-line determination of the ozone
concentration as function of the height. This information can be delivered in form of ASII files or
as graphical tables. Technical specification for the Elight Ozone Profiler is available at their web
site at http://www.elight.de/profiler2.htm.
C-8