Readme file for DRI CCN There are presently two types of files for each day (as defined by universal time). These are all from the C-130 during the deployment from Hobart (Nov. 17-Dec. 12). We hope to complete the transit flights at some later time. We are also working on another set of files that excludes the measurements that were obtained within clouds. As some of you are well aware there are two sets of problems with in cloud aerosol data. Based on past experience there is often splashing of cloud droplets in sample inlets that often led to spurious CN and/or CCN counts. This was not always a problem in ACE-1 but it probably sometimes was a problem. The second problem of in cloud measurements is that to some extent these are cloud interstitial measurements because many of the cloud droplets are excluded from the sample. This is most relevant to CCN because they are expected to be within the cloud droplets. This could be a useful measurement if we knew the cutoff size, but we do not. As a result of these two factors the in cloud measurements can be confusing. There is further confusion because there were often rather high CN and CCN concentrations in the air just above cloud top. It is often difficult to separate these measurements from the in cloud measurements. The concentrations that are given are normalized to sea level pressure. They are concentrations per cubic centimeter normalized to sea level pressure. This is the case for both the CCN and CN measurements. In the case of the CCN this is directly obtained because a mass flowmeter was used to measure the sample into this cloud chamber. For the CN measurements a constant volume flow was maintained in the TSI 3010 as is best for optimal operation. Then the concentrations were all multiplied by (1000/measured pressure in mb). The pressure used here was the one measured with our own little sensor (column 14 of the data files), which was monitoring the pressure in the sample tube between the community inlet and our instruments. This measurement only approximates the actual ambient pressure. The CCN spectra are presented in cumulative concentrations; it is the number of particles with critical supersaturations at or below the value given at the top of the column. Thus in any time period the concentrations should decrease (or be the same) from the left columns (1%) to right (0.02%). The third column is a total CCN concentration at some unspecified supersaturation above 1% (it is usually very close to 1%). The CN concentration should equal or exceed the total CCN concentration. The measurements in the instruments are delayed. The CCN lags the CN by about 30 seconds but there is some variability in this lag due to differences in flows due to altitude changes and due to deliberate changes in sample flow rates. We do not know the lag time of the CN counter but it should not be much more than a second or a few seconds. We have not yet made any corrections for time lags of the instruments. The time given here was not the same as the aircraft time. We attempted to keep it within 1 sec of aircraft time--this is the best we could do. The data presented here are ambient, unprocessed measurements. All other measurements that were obtained during the project have been removed from these files. At least we attempted to remove them. Processing consisted of: 1) heating the sample to determine particle volatility; and 2) size classifying the sample to determine size vs. Sc. These data will be treated separately and probably not archived; at least not for quite a while. Another reason for gaps in the data was that calibrations were done at least once per flight. There were also occasional malfunctions of the instruments. If you have any questions please email (hudson@sage.dri.edu) or call 702-677-3119 or fax 702-677-3157. Jim Hudson.