****Instructions for running Kasting group's 1-D photochemical code****
                   by Pushker Kharecha, March 2005
	(last actualization by antigona Segura, August 2006)


This code pertains to an anaerobic Archean biosphere (pre-oxygenic 
photosynthesis). It is written largely in Fortran 77 with some Fortran 
90 features, and is formatted to run on a Sun (unix) system

BEFORE compiling the code check the make file make_photoco2. The commands:
-xtarget=ultra -xarch=v9 are system dependent. Check that your system supports
this ptions or chenge them for their equivalent on your system, otherwise you
may create a excecutable file that is not excecutable for your system. 

To run the program, we use a script file (filename.q). This file simply 
contains the UNIX command sequences for compiling and running the program 
over our particular network.

The script file is used as follows: From the directory that contains the code
and all of  its input files, type in:
./filename.q &
at the  command prompt, where "filename" is the name of the script file and
the  "&" symbol runs the process in the background.

Almost all  input files have a ".DAT" extension, and output files have a ".dat"
or  "out" extension. 

A crucial component of this code is calculation of the planetary H2 budget 
(i.e., electron budget). It contains a method of iteratively adjusting the  H2
volcanic outgassing rate, which appears just after the start of the main 
time-stepping loop. This is relevant only if users are including organisms 
that depend directly or indirectly on H2 (in the case for this code,  H2-using
anoxygenic phototrophs and CO-using acetogens). Users can simply  comment out
these lines if they want the planetary H2 balance to be only  between H2
outgassing and escape to space, i.e., if they want to neglect C _org burial. 

Another very important element is the lower boundary condition on  atmospheric
constituents. For our purposes, we've used constant  deposition velocity for H2
and CO in order to reflect the coupling  with the ecology in this particular
ecosystem (one in which the  primary producers are H2-using anoxygenc
phototrophs and CO-consuming  acetogens). If constant mixing ratio is used for
H2, and if users are  simulating a methanogenic ecosystem, then they must
adjust the H2  mixing ratio until they obtain ~equal H2 deposition velocities
from  both the photochemical model and the ecosystem model -- these can be 
tracked in the output file via the values for VPHOTO(H2) and VECO(H2).

This program also contains our ecosystem code, which exists as a set  of
subroutines near the end of the overall program. If users are not  planning to
incorporate ecology and want a simpler output file, they  can simply comment
out the corresponding call statements in the main  code (CALL H2aq, etc). 


References
Kharecha, P., Kasting, J.F., and Siefert, J.L (2005) A coupled
atmosphere-ecosystem model of the early archean Earth. Geobiology 3, 53-76.