ASOPOS (Assessment of Standard Operating Procedures (SOPs) for OzoneSondes) 2.0: Measurement Principles and Best Operational Practices for Ozonesondes

The ozonesonde is a small balloon-borne instrument that is attached to a standard radiosonde to measure ozone profiles from the surface to 35 km with 100-m vertical resolution. The electrochemical-concentration cell (ECC) ozonesonde has been used at ~100 stations worldwide for over 50 years. There are two types of ECC ozonesonde and three different chemical sensing solutions used within the sonde network that affect the ozonesonde measurement and introduce a number of random and systematic uncertainties in ozonesonde records. Since 2004, the WMO/GAW-sponsored ASOPOS (Assessment of Standard Operating Procedures (SOPs) of OzoneSondes) team of experts has been evaluating ozonesonde records and the results of field and laboratory experiments that intercompare instruments. The first ASOPOS Guidebook for best practices was published in the WMO/GAW Report 201 [Smit et al., (2014)]. At the urging of the ozone trends community, the ASOPOS team has worked on a new set of recommendations that are being published as the ASOPOS 2.0 Report. We summarize important aspects of the new report: 1) the measurement principles of the ozonesonde instrument, 2) the uncertainty chain of the parameters affecting the measurement, 3) new recommendations on sonde preparation steps and 4) revised data processing protocols. Newly added sections give expanded guidelines on data quality indicators and the rationale for the recording of enhanced metadata. With the adoption of these SOPs, the global ozonesonde community has the potential to achieve the 5% uncertainty level in tropospheric and stratospheric ozone requested by the satellite and trends communities.