Comparison with other size distributions of PBAP

Ž . distributions d nrdlog r of the total number of insoluble particles small symbols and of Ž . Ž . Ž biological particles big symbols from 0700–0800 h cross and 1900–2200 h up . Ž . triangle referred to milliliter of cloud water and their corresponding percentage dotted in each size class. You see that the concentration increased with time. This is mainly Ž caused by spores see the relative maximum in the percentage curve with about 40 in . Ž . the 3rd radius interval and plant debris with up to 90 in the 8th and 9th interval . Even the number of MO increased. Looking at the meteorological conditions during that event, we had an increase of wind velocity producing strong defoliation, which could explain the growing concentration of bacteria and of plant debris. The second event we analysed was on the 7th and 8th of Nov. and lasted about 27 h Ž . and we analysed samples of the first 7r11, 1720–1800 h and of the second half Ž . 8r11, 0700–0800 h . The results are seen in Fig. 3. Prior to this event, we had a dry, Ž . cold T - 08C period with strong defoliation. This is seen in the concentration of the Ž . Ž . giant particles 7r11 see percentage curve , where we first of all found plant debris and pollen, which were deposited on the leafs and got resuspended into the atmosphere through this defoliation. Later, within the cloud event, the temperature increased while Ž . Ž . the wind velocity decreased 1 mrs . We found now 8r11 more MO and less plant debris and pollen. Looking at both events, the percentages of PBAP per milliliter cloud water increased from 17–25 up to 40–41 during one event. Ž . In the next cloud event we will consider, it started on the 13th of Nov. see Fig. 1 and lasted 39 h. Fig. 4 shows the size distributions of two samples collected in the Ž . Ž . middle 2100–2400 h and at the end 14r11, 1100–1400 h of this event. The concentrations of the total particles were one order of magnitude larger and even the concentration of PBAP was twice of that compared to the previous events. The whole Ž . sampling period was largely influenced by the Rhine-Main region southern winds , which leads to this increase of the total, as well as of the biological particles, first of all Ž . MO. This effect anthropogenic influence leads to an increase of MO was found also in Ž . the ground based measurements Matthias-Maser and Jaenicke, 1995 . However, the percentages did not change during the whole event.

5. Comparison with other size distributions of PBAP

5.1. Size distributions in the liquid phase Ž . Matthias-Maser et al. 1996 determined the size distribution in rainwater samples collected in Mainz. We calculated the mean values for PBAP related to milliliter of Ž . cloud water and compared it to the values in rainwater Fig. 5 . Here, a difference between the two size distributions of sometimes more than two orders of magnitude is seen. Ž . This is also obvious in the mean concentrations Table 1 . The content of biological particles in cloud water lies over three orders of magnitude higher than in rainwater; regarding the volume, the difference is only two orders of magnitude. This effect originating from the stronger dilution of the particles in rainwater was also found by Ž . Schutz and Kramer 1987 for the total particles. ¨ ¨ Fig. 5. Mean size distributions in rainrcloud water. 5.2. Size distributions in the gaseous phase During some cloud events, the surroundings of the KFB was cloud-free and syn- chronous aircraft measurements were performed at about an 800-m altitude around the KFB outside of the clouds. For the determination of PBAP in dry air, the aircraft was Ž . equipped with a slit-impaction system Gruber, 2000 . Unfortunately, no direct compari- son between the three size distributions of PBAP was possible because of the weather Ž . situation no upwind–downwind situation , but the results give a first guess of the Table 1 Mean concentrations of PBAP for cloud water and rainwater referred to ml y1 , in brackets the percentage of the total particles cloud 7 y1 cloud 7 3 y1 Ž . Ž . N s 0.105=10 ml 24 V s1.318=10 mm ml 12.3 bio bio rain 3 y1 rain 5 3 y1 Ž . Ž . N s 3.57=10 ml 9 V s 4.61=10 mm ml 48 bio bio biological content in the atmospheric aerosol in about an 800-m altitude within and outside the clouds. Fig. 6 shows the mean size distributions of these flight measurements Fig. 6. Size distributions of PBAP. Table 2 Mean concentrations of PBAP for Mainz, 800-m altitude and cloud water referred to cm y3 Ma inz y3 Mainz 3 y3 Ž . Ž . N s 3.1 cm 23.7 V s6.5 mm cm 22.3 bio bio 800 m y3 800 m 3 y3 Ž . Ž . N s 0.196 cm 14.4 V s1.68 mm cm 20.9 bio bio cloud y3 cloud 3 y3 Ž . Ž . N s 0.0198 cm 25.0 V s 0.29 mm cm 11.7 bio bio Ž . upper triangle together with the model size distributions for total, rural aerosol Ž . Ž . Ž Jaenicke, 1988 thick, solid line and PBAP of urbanrrural influenced region Mat- . Ž . thias-Maser, 1998 thin, solid line . In addition, we calculated the mean size distribution Ž . of PBAP in cloud water cross , referring to cubic centimeter of air volume, from which the cloud water samples originate. As a first result, we found PBAP in this altitude, which lay between 1 and 1.5 orders of magnitude higher in concentration than those of PBAP in the cloud water samples and one order of magnitude lower for the particles with r - 10 mm than those of the ground-based measurements. However, in Fig. 6, the seasonal peculiarities are obvious. The sampling period of the flight measurements and of the cloud water samples was autumn, with an enlarged occurrence of plant debris. Compared to the ground measurements, which show a yearly average, the size distribution of PBAP for the particles with r 10 mm in radius at an 800-m altitude lay above the ground measurement. This seasonal effect is also seen in the total concentrations N V , and N V , tot tot bio bio respectively, listed in Table 2 showing the mean values for Mainz, for the 800-m altitude and for cloud water. Fifteen percent of the number concentrations at an 800-m altitude were biological, whereas over 20 in volume were PBAP. Looking at the insoluble particles found in cloud water about 25 in number and 12 in volume concentration were PBAP.

6. Conclusions