
I frequently work with hourly data in GMT format, and ensure that any data I
read into R are expressed in GMT through as.POSIXct(mydate, tz = "GMT"). 

I am interested in processing air pollution data in GMT where where peaks in
emissions (say from road traffic sources) tend to occur at the same LOCAL
time each day.  I am interested in calculating mean concentrations by hour
of day i.e. a diurnal profile, consisting of 24 hourly means.  The profile
would be clearer if all hours were in local time e.g. the daylight saving
hours were shifted by +1 hour.  This would ensure that the summer and winter
profiles match up with those in emissions.

I've looked though the various R documents/forum, but can't seem to identify
the easiest approach to this.

Any suggestions?

Many thanks.

David
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