Inconsistency in treatment of undefined environmental variables between SMOKE ASSIGNS_FILE and IOAPI ENVYN

[hnqtran]

Currently upon source $ASSIGNS_FILE is called in SMOKE, several controlling environmental variables (e.g., DAY_SPECIFIC_YN, HOUR_SPECIFIC_YN, SMK_PING_METHOD, etc.) are assigned with ' ' (blank space; length = 1) if they were not defined in the run scripts when $ASSIGNS_FILE calls check_settings.csh.

These controlling variables are then queried in SMOKE program using IOAPI function ENVYN(). Per ENVYN() documentation, undefined environmental variable are supposed to assigned with default values and return In/Out status (IOS) = -2.

However, since these controlling variables are assigned with ' ' by $ASSIGNS_FILE in earlier step, ENVYN() realizes these variables as defined but with unrecognized value. Consequently, ENVYN() applies default values to these variables but return IOS = 1.

Implementing hard QA check in SMOKE for proper values of controlling environmental variables (e.g., hafting SMOKE execution if ENVYN() return IOS = 1 when check on DAY_SPECIFIC_YN) requires modifications to how check_settings.csh handle undefined environmental variables

[cjcoats]

What is actually needed is changing the SMOKE source so that it correctly checks the status of all env*() calls.

This is in fact a large and tedious effort, which was done (among other things) and supplied to EPA in
https://github.com/cjcoats/SMOKE-m3utilio

[cjcoats]

See https://cjcoats.github.io/ioapi/ENVGETS.html:
empty-string is NOT a valid value for any of the env routines nor is it a case of "undefined".