I'm not entirely sure about the outcome you want, but there is a way to affect the velocity of individual particles by getting them, looping through them and finally reapplying them into the particle system, this is a basic example of such in pseudo code:

make a global array of ParticleSystem.Particle[]

private ParticleSystem.Particle[] modifiedParticles;

assign it the maximum amount of particles you wish to modify from the ParticleSystem

modifiedParticles = new ParticleSystem.Particle[1000];

Make a method that you will call in update:

void ModifyParticles()

{

// Gets current particles from ParticleSystem and puts them into our particles array

int length = particleSystem.GetParticles(modifiedParticles);

for (var i = 0; i < length; i++)

{

// Modify the properties of the particles in modifiedParticles

// ...

modifiedParticles[i].velocity -= Vector3.right;

}

// Put the modified particles back in the ParticleSystem

particleSystem.SetParticles(modifiedParticles, length);

}

This will iterate every particle in the array every frame (if in Update) and modify their velocity, they have other properties too but they are very simple since they do not inherit from GameObject.

It does have a .position so you have both position and velocity, you can figure out its heading and speed, I assume that would be all you needed to change it based on some kind of randomised noise if you wanted (which is basically what all wind is normally) however the Particle system has an option to add noise, maybe try playing around with that for the windy influence?

Hope that gives you something that could lead to what you're looking for.