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Ground-level ozone pollution
Ground-level ozone (O3), when in high concentrations, is regarded as an air pollutant and is often found in smog in industrial areas. O3 is largely produced by chemical reactions involving NOx gases (nitrous oxides, especially from combustion) and volatile organic compounds in the presence of sunlight.

There is limited research pertaining to the effect that ozone pollution does have on fertility (Conforti et al 2018). At present, there is no evidence to suggest that ozone exposure poses a deleterious effect on spontaneous fertility in either females or males. However, there have been studies which suggest that high levels of ozone pollution (often a problem in the summer months) do exert an effect on in vitro fertilisation (IVF) outcomes. In fact, within an IVF population, NOx and ozone pollutants were linked with reduced rates of live birth (Conforti et al 2018).

Furthermore, whilst most research on this topic is focused on the direct human exposure of air pollution, other studies have analysed the impact of air pollution on gametes and embryos within IVF laboratories. Multiple studies have reported a marked improvement in embryo quality, implantation and pregnancy rates after IVF laboratories have implemented air filters in a concerted effort to reduce levels of air pollution (Frutos et al 2014). Therefore, ozone pollution is considered to have a negative impact on the success of assisted reproductive technologies (ART) when occurring at high levels.

However, ozone is thought to act in a biphasic manner where a positive effect on live birth is observed when ozone exposure is limited to before IVF embryo implantation (Checa Vizcaíno, Miguel A., Mireia González-Comadran, and Benedicte Jacquemin. “Outdoor Air Pollution and Human Infertility: a Systematic Review.” Fertility and sterility 106.4 (2016): 897–904.e1. Web). Conversely, a negative effect is demonstrated upon exposure to ozone after embryo implantation (Carré et al 2017).

In addition to this, retrospective and prospective studies evaluating the effect of several traffic pollutants (of which ground-level ozone is one) highlighted a significant decrease in live birth rates and miscarriages (Frutos et al 2014).

In terms of male fertility, ozone is reported to cause a significant decrease in sperm concentration measured in semen after exposure ( https://rdcu.be/cWWgF ). Similarly, sperm vitality (the proportion of alive spermatozoa in a sample) was demonstrated to be diminished in a handful of studies (Carré et al 2017). This demonstrates that ozone air pollution exhibits a significantly negative effect of air pollution on this parameter. However, findings on the effect of ozone exposure on male fertility are somewhat discordant, highlighting the need for further research (Carré et al 2017).