be applied in heat transfer equipment with low refrigerant charge such as brazed plate heat exchangers (BPHE), or shell and tube heat exchangers and tube and plate heat exchangers with tube of small diameter. Many applications confirmed that difluoromethane exhibits heat transfer coefficients higher than those of R-410A under the same operating conditions but also higher frictional pressure drops. Other uses of difluoromethane include its use as aerosol propellants, blowing agents, and solvents. Environmental Effects Every year, approximately 15 kilotons of difluoromethane are produced. In gas form, the compound will degrade in the atmosphere by reaction with photochemically-produced hydroxyl radicals. This process will form carbonyl difluoride. The half-life for this process is estimated to be 4 years. Difluoromethane tends to enter the environment via the gas phase and accumulates there more commonly than in soils or sediments. Volatilization half-lives of this compound are about 45 minutes for rivers and 69 hours for lakes, difluoromethane does not bioaccumulate in aquatic areas well. HFC-32 released into the environment gets broken down into CF as an intermediate product. This goes on to create HF and CO2 by hydrolysis in atmospheric water. The global warming potential (GWP) of HFC-32 is estimated at 677 on a 100-year time window. This is far lower than the GWP for HFC refrigerants it is replacing, but remains sufficiently high to spur continued research into using lower-GWP refrigerants. Difluoromethane is excluded from the list of VOCs supplied in the United States Clean Air Act due to the ODP being zero. Therefore, tropospheric ozone is not likely to be produced from this molecule. Tropospheric ozone may lead to adverse health effects such as respiratory, cardiac or neurological damage. Additionally, ozone can affect plant and vegetation by inducing the bronzing of leaves. Toxicity Difluoromethane shows slight maternal and developmental toxicity at concentrations of approximately 50,000 ppm in rats, but not in rabbits. The exposure limitations set on difluoromethane for human use are 1,000 ppm, making exposure to dangerous levels unlikely. References External links Flammability Measurements of Difluoromethane in Air at 100 °C Difluoromethane at Gas Encyclopaedia IR absorption spectra SDS Data sheet Fluoroalkanes Halomethanes Refrigerants