Pk. Hopke et al., COMBINING CHEMICAL AND METEOROLOGICAL DATA TO INFER SOURCE AREAS OF AIRBORNE POLLUTANTS, Chemometrics and intelligent laboratory systems, 19(2), 1993, pp. 187-199
Models have been developed to identify and quantitatively apportion th
e contributions of sources to the measured concentrations of airborne
constituents. These models have generally been applied to local, urban
scale problems in which the differences in the patterns of elemental
concentrations in the emissions of different sources are used to parti
tion aerosol mass to the identified sources. However, these models do
not provide information on the locations of the sources. New approache
s are thus needed to find specifically where airborne contaminant emis
sion sources can be found. Using models of atmospheric transport, mete
orological information in the form of air parcel back trajectories can
be calculated. The trajectories are presented as a series of location
s where the air parcels that deliver material to a given sample were a
t fixed intervals, backwards in time. If the area covered by these end
points is divided into a gridded array, the amount of time spent in a
cell is related to the number of endpoint segment locations that fall
into that cell. The ratio of the number of endpoints related to high c
oncentration samples to the total number of endpoint that fall into th
e cell can be considered to be the conditional probability that the pa
rticular grid cell was a source of the species found in high concentra
tion. This probability is called the potential source contribution fun
ction (PSCF). This approach has been applied to three problems of iden
tifying the sources of secondary sulfate in particles at different sca
le lengths; sub-regional, regional, and semiglobal. At a sub-regional
scale in the Los Angeles area of southern California, PSCF analysis wa
s applied to measured SO2 and SO42- measured at one site downwind of L
os Angeles. Transport of particulate SO42- to Dorset, Ontario was obse
rved on a regional scale, and non-marine sulfate contributions to samp
les collected in the high Arctic were examined on a semi-global scale.
In all cases good agreement was found between the high PSCF cells and
previously identified source areas. In each case the analysis helped
to provide an improved understanding of the source-receptor relationsh
ips for the particular scale length.