Sunday 19 th June 2005 – a potentially interesting case study from Cityflux. Focus is a torrential downpour in the afternoon. All times GMT. Below: half-hourly wind speed, direction and temperature from the Airport. RH (not shown) jumps from ~60% to 100% around 3pm, only falling after 6pm. Note that wind initially S, then strong gust corresponding to veer to WNW, then quite rapid deceleration. This deceleration is more rapid in city centre

By 15:15 wind is WNW, ~ ms-1. Strong spike seen in particle numbers >0.3mm (Grimm), affecting all size channels at Maybrook House (Deansgate). 10 minutes later smaller spike in Grimm at Whitworth Street (room B18a). Grimm in J1 peaks, but no spike.

This spike (15:15-15:25) coincides with huge volume of rainfall, as recorded by PWS on Pariser roof:

Over next 1.5 hours particle numbers rise at all monitors. Another major shower observed at 16:47 – 17:05. This coincides with second spike at Maybrook House, plus peaking of particle numbers at our building (but no spikes). Grimms might be seeing rain spray.

Preceding these events gas and PM10 levels at Piccadilly are rising (except O3), whereas after 4pm they are all falling, with exception of PM10 spike at 19:00.

Clear dip in AMS data during the first shower, although rise preceding it, appearing to coincide with arrival of gust front? After first shower, however, strong rise so that levels end higher than earlier (~ 1pm). Ammonia is roughly halved by the shower. Note that before the shower NH3 was unusually high.

So, what was going on? Gas-particle conversion? Does anybody have any further data to add to the mix, or any insights, or suggestions of things to look for. I am hoping that a)This will help inform some of the processes affecting the TDL ammonia data, contributing to Jamie’s thesis and my paper on the TDL which requires more explanation of observed patterns, and b)Possibly a separate paper on this day as a case study