datablock ParticleData(Snow1Particle)
{
dragCoefficient = 0;
gravityCoefficient = 0.2;
inheritedVelFactor = 0.0;
constantAcceleration = 0.0;
lifetimeMS = 3080;
lifetimeVarianceMS = 0;
textureName = "./snow1";
spinSpeed = 0.0;
spinRandomMin = 00.0;
spinRandomMax = 00.0;
colors[0] = "1.0 1.0 1.0 0.0";
colors[1] = "1.0 1.0 1.0 1.0";
colors[2] = "1.0 1.0 1.0 1.0";
colors[3] = "1.0 1.0 1.0 0.0";
sizes[0] = 0.30;
sizes[1] = 0.30;
sizes[2] = 0.30;
sizes[3] = 0.30;
windCoefficient = 0.0;
times[0] = 0.0;
times[1] = 0.05;
times[2] = 0.99;
times[3] = 1.0;
useInvAlpha = true;
};
this line would be your best option. this changes how long the rain particle lasts before it disappears (3080 meaning the particle lasts 3.08 seconds, obviously.)
also note that an emitter has a particle datablock and emitter datablock which are two different things. this code is from the particle datablock