VOCs are gasses that combine with other substances to form ground level ozone (smog). In an effort to reduce smog in the San Joaquin Valley, as of Nov 1, the Department of Pesticide Regulation (DPR) is restricting sales and use of High-VOC producing ag products during the months of May through October. High-VOC ag products have an emission potential (EP) greater than 35%. For citrus, products of concern include chlorpyrifos, gibberellin, abamectin and oxyfluorfen. There are many formulations of each of these agricultural products and the goal is to choose formulations that keep the EP below 35%. The following link provides a list of the formulations that are above (High-VOC) and below (Low-VOC) the EP threshold of 35% for all crops. Keep this in mind as you purchase and use insecticides, herbicides and gibberellin.
DPR Overview http://www.cdpr.ca.gov/docs/emon/vocs/vocproj/factsheet_voc_overview.pdf
List of High and Low-VOC formulations http://www.cdpr.ca.gov/docs/emon/vocs/vocproj/nonfum_voc_prod_list.pdf