Environment occlusion - when this option is checked V-Ray will use the environment when calculating the occlusion of areas that are not occluded by other objects.
Affect Reflection - when checked the ambient reflection will affect the reflection render elements. This can be used to create reflection masks
Ignore Self Occlusion - when this option is on the object will not occlude itself. It will still be occluded by other objects in the scene.
Double_Sided - when enabled the rays needed to generate the dirt map will be shot from both sides of the faces( both in the direction of the normals and in the opposite direction)
Ignore other objects - when on, the dirt will affect only the objects themselves, without including contact surfaces and edges. If off, the entire scene geometry is participating for the final result.
Use Transparency - when on, VRayDirt will take into account the opacity of the occluding objects. This can be used, for example, if you want to calculate ambient occlusion from opacity-mapped trees etc. When off (the default), occluding objects are always assumed to be opaque. Note that working with correct opacity is slower, since in that case VRayDirt must examine and evaluate the material on the occluding objects.
Black - this is the color that will be returned by the texture for occluded areas. You can also use a texture map for this parameter.
Glossiness - this parameter controls the spread of the rays traced for reflection occlusion. You can also use a texture map for this parameter.
White - this is the color that will be returned by the texture for unoccluded areas. You can also use a texture map for this parameter.
Subdivs - controls the number of samples that V-Ray takes to calculate the dirt effect. Lower values render faster but produce a more noisy result.
Example: Subdivisions Parameter