VOCs and POCPs

HFCs/HFOs and HCFOs have negligible contribution to ground-level ozone formation

What is photochemical smog: Some organic compounds, in the presence of sunlight and NOx, take part in ground-level ozone formation and thereby contribute to the deterioration in regional and urban air quality, with adverse effects on human health and environment.


Photochemical Ozone Creation Potential (POCP)

Each organic compound exhibits a different propensity to form ozone, which can be indexed in a reactivity scale, the Photochemical Ozone Creation Potential (POCP). The concept of the Photochemical Ozone Creation Potential (POCP) is a widely used approach to estimate the relative importance of individual VOCs for the short-term production of ground level ozone (O3). https://www.eea.europa.eu/publications/TOP08-98/page004.html

In Europe, POCP is used to address long-range transboundary formation and transport of ozone. The alkanes (ethane, propane and isobutane) and alkenes (ethylene and propylene) exhibit steadily increasing reactivities from ethane, which is unreactive, to propylene, which is highly reactive. Alkanes generate ozone efficiently on the multi-day scale. 

EU definition: Non-methane volatile organic compounds (NMVOCs) are a collection of organic compounds that differ widely in their chemical composition but display similar behaviour in the atmosphere. NMVOCs contribute to the formation of ground level (tropospheric) ozone. Source https://www.eea.europa.eu/data-and-maps/indicators/eea-32-non-methane-volatile-1

In the USA: A compound may be excluded as a VOC as a result of scientific data that demonstrates its negligible effect on the formation of ground-level ozone. The EPA uses the reactivity of ethane as the threshold for determining whether a compound has negligible reactivity. Compounds that are less reactive than, or equally reactive to, ethane under certain assumed conditions may be deemed negligibly reactive and, therefore, suitable for exemption from the regulatory definition of VOC.

References:
IPCC/TEAP Special Report Safeguarding the Ozone Layer and the Global Climate System: Issues Related to Hydrofluorocarbons and Perfluorocarbons Chapter 2 page 169 and Atmospheric chemistry of short-chain haloolefins: Photochemical ozone creation potentials (POCPs), global warming potentials (GWPs), and ozone depletion potentials (ODPs), T.J. Wallington M.P. Sulbaek Andersen and O.J. Nielsen Chemosphere Volume 129, June 2015, Pages 135-141, https://doi.org/10.1016/j.chemosphere.2014.06.092

Volatile Organic Compounds (VOCs)