What factor does NOT increase volatility of herbicides?

Volatility in herbicides refers to the tendency of the chemicals to evaporate into the air. High air temperature and low relative humidity are both factors that enhance volatilization; they create conditions that promote the rapid transition of the herbicide from a liquid to a gas. A high air temperature increases the kinetic energy of the molecules, making it easier for them to escape into the air. Low relative humidity means that the air is drier, which can also encourage evaporation.

In contrast, high humidity works against this process because it means there is already a lot of moisture in the air. This higher moisture content reduces the evaporation rate of the herbicide, which means that volatile chemicals are less likely to transition from liquid to vapor. Thus, high humidity actually serves as a factor that decreases the volatility of herbicides, making it the right choice for the question regarding what does not increase volatility.

Additionally, small nozzle orifice size can affect the droplet size and application pattern, which may influence the distribution of the herbicide but does not directly increase its volatility. Hence, it does not belong in the context of the factors that enhance volatility like the others do.