openair package. Files are imported from a remote
server operated by AEA that provides air quality data files
as R data objects.importSAQN(site = "gla4", year = 2009, pollutant = "all")site = c("gla4", "ed") --- to import Glasgow
Kerbside and Edinbrugh Centre for example.year = 1990:2000.
To import several specfic years use year = c(1990,
1995, 2000) for example.pollutant = c("nox",
"no2").importSAQN function has been written to make it
easy to import data from the Scottish Air Quality Network
(SAQN) ---
There are several advantages over the web portal approach
where .csv files are downloaded. First, it is quick to
select a range of sites, pollutants and periods (see
examples below). Second, storing the data as .RData objects
is very efficient as they are about four times smaller than
.csv files --- which means the data downloads quickly and
saves bandwidth. Third, the function completely avoids any
need for data manipulation or setting time formats, time
zones etc. Finally, it is easy to import many years of data
beyond the current limit of about 64,000 lines. The final
point makes it possible to download several long time
series in one go. The function also has the advantage that
the proper site name is imported and used in openair
functions.
The site codes and pollutant names can be upper or lower case. The function will issue a warning when data less than six months old is downloaded, which may not be ratified.
The data are imported by stacking sites on top of one
another and will have field names site, code
(the site code) and pollutant. Sometimes it is
useful to have columns of site data. This can be done using
the reshape function --- see examples below.
All units are expressed in mass terms for gaseous species (ug/m3 for NO, NO2, NOx (as NO2), SO2; and mg/m3 for CO). PM10 concentrations are provided in gravimetric units of ug/m3 or scaled to be comparable with these units. Over the years a variety of instruments have been used to measure particulate matter and the technical issues of measuring PM10 are complex. In recent years the measurements rely on FDMS (Filter Dynamics Measurement System), which is able to measure the volatile component of PM. In cases where the FDMS system is in use there will be a separate volatile component recorded as 'v10', which is already included in the absolute PM10 measurement. Prior to the use of FDMS the measurements used TEOM (Tapered Element Oscillating. Microbalance) and these concentrations have been multiplied by 1.3 to provide an estimate of the total mass including the volatile fraction.
The few BAM (Beta-Attenuation Monitor) instruments that have been incorporated into the network throughout its history have been scaled by 1.3 if they have a heated inlet (to account for loss of volatile particles) and 0.83 if they do not have a heated inlet. The few TEOM instruments in the network after 2008 have been scaled using VCM (Volatile Correction Model) values to account for the loss of volatile particles. The object of all these scaling processes is to provide a reasonable degree of comparison between data sets and with the reference method and to produce a consistent data record over the operational period of the network, however there may be some discontinuity in the time series associated with instrument changes.
No corrections have been made to teh PM2.5 data. The volatile component of FDMS PM2.5 (where available) is shown in the 'v2.5' column.
While the function is being developed, the following site codes should help with selection.
importAURN for data elsewhere in the UK
and importKCL for importing comprehensive
data in and around London.## import all pollutants from Glasgow Roadside
glas <- importSAQN(site = "gla4", year = 2000:2009)
## import all pollutants from Lerwick rural site (O3)
ler <- importSAQN(site = "lerw", year = 2005:2010)
## import all pollutants from Glasgow/Dundee Centre for 2009
all <- importSAQN(site = c("gla3", "dun3"), year = 2009)Run the code above in your browser using DataLab