Documentation of the Evaluation of CALPUFF and Other Long ...

The puff splitting flag (item 2) is turned on using the IRESPLIT input option. IRESPLIT consists of
24 values corresponding to the hour of the day with values that are either 0 or 1, where 1 turns
on the puff splitting flag for puffs. Once the puff splitting flag is turned on, it remains on until
the puff splitting occurs at which point the puff splitting flagged is turned off until it is turned
back on again by IRESPLIT. The default setting for IRESPLIT is to have all hours zero except for
setting hour 17 to 1. The reasoning behind this is to invoke puff splitting in the evening when a
nocturnal inversion occurs and there is a decoupling of the winds between the nocturnal
inversion layer and above the nocturnal inversion (i.e., the residual “mixed layer”). Setting
IRESPLIT to all zeros will result in the puffs never performing vertical puff splitting and setting
IRESPLIT to all ones will result in the puff splitting flag always turned on and puffs will always
split when the other three criteria for vertical puff splitting are met.
The default value for the previous hours minimum mixing height value (item 3) is ZISPLIT = 100
m. This minimum value is used to assure that the current mixing height is not negligible.
The ratio of the previous hours mixing height to maximum mixing height encountered by the
puff (item 4) is controlled by the ROLDMAX parameter with a default value of 0.25.
When vertical puff splitting occurs in CALPUFF, the number of puffs that the puff is split into is
controlled by the NSPLIT parameter that has a default value of 3.
Horizontal puff splitting occurs when the puff concentrations are above a minimum value
(CNSPLITH), the puff has a minimum width that is defined by its sigma‐y in grid cell units
(SYSPLITH) and the minim puff elongation rate (SYSPLITH per hour) is above a SHSPLITH factor.
The default minimum concentration is CNSPLITH = 10 ‐7 g/m 3 (0.1 µg/m 3 ). Default SYSPLITH
value is 1.0 and default SHSPLITH factor is 2.0. When horizontal puff splitting occurs in
CALPUFF the number of puffs the puff is split into is controlled by the NSPLITH parameter that
has a default of 5.
Eight CALPUFF puff splitting sensitivity tests were conducted, which are defined in Table 6‐3.
When vertical and horizontal puff splitting occurs in CALPUFF, the default number of puffs to
split into was used in the CALPUFF sensitivity tests (i.e., NSPLIT = 3 and NSPLITH = 5). The
NOSPLIT sensitivity test set MSPLIT = 0 so no vertical or horizontal puff splitting was allowed to
occur. The DEFAULT puff splitting turned on puff splitting (MSPLIT = 1) but only turned on the
vertical puff splitting flag at hour 17 every day. Whereas, the ALLHRS sensitivity test made sure
that the vertical puff splitting flag was turned on all the time (i.e., IRESPLIT = 24*1) removing
criteria 2 from the vertical puff splitting requirement. The ZISPLIT sensitivity test set ZISPLIT to
zero thereby removing criteria 3 in the vertical puff splitting, as well as requirement 2 (like
ALLHRS). ROLD relaxed the minimum ratio of the previous hours to maximum mixing height for
vertical puff splitting from 0.25 to 0.50. The SYS sensitivity test allows horizontal puff splitting
to occur more frequently by allowing puff splitting to occur with a puff sigma‐y value is greater
than SYSPLITH values of 0.1 (2.6 km) versus the default 1.0 (36 km) value. The last sensitivity
test combines the ROLD and SYS sensitivity tests.
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