Measurements of O3, NO2 and BrO during the INDOEX campaign using ground based DOAS and GOME satellite data

摘要

The INDian Ocean EXperiment (INDOEX) was aninternational, multi-platform field campaign to measure long-rangetransport of air masses from South and South-East-(SE) Asiatowards the Indian Ocean. During the dry monsoon season betweenJanuary and March 1999, local measurements were carried out fromground based platforms and were compared with satellite baseddata. The objective of this study was to characterisestratospheric and tropospheric trace gas amounts in the equatorialregion, and to investigate the impact of air pollution at thisremote site. For the characterisation of the chemical compositionof the outflow from the S-SE-Asian region, we performed groundbased dual-axis-DOAS (Differential Optical AbsorptionSpectroscopy) measurements at the KCO (Kaashidhoo ClimateObservatory) in the Maldives (5.0° N,73.5° E). The measurements were conducted using twodifferent observation modes (off-axis and zenith-sky). Thistechnique allows the separation of the tropospheric andstratospheric columns for different trace gases like Oand NO. These dual-axis DOAS data were compared withO-sonde measurements performed at KCO and satellite basedGOME (Global Ozone Measuring Experiment) data during the intensivemeasuring phase of the INDOEX campaign in February and March 1999.From GOME observations, tropospheric and stratospheric columns forO and NO were retrieved. In addition, theanalysis of the O-sonde measurements allowed thedetermination of the tropospheric O amount. Thecomparison shows that the results of all three measurement systemsagree within their error limits. During the INDOEX campaign,mainly background conditions were observed, but in a single casean increase of tropospheric NO during a short pollutionevent was observed from the ground and the impact on the verticalcolumns was calculated. GOME measurements showed evidence forsmall tropospheric contributions to the BrO budget,probably located in the free troposphere and present over longperiods of the year. The amounts of BrO have beeninvestigated by the comparison of satellite pixels influenced byhigh and low cloud conditions based on GOME data which allows thedetermination of the detection limit of3.8×10molecules cm of tropospheric BrOcolumns.