This image, from Punch magazine in July 1858 is in reference to the horrible smells that came from the river Thames. Due to poor sewage, the massive population growth, and industrial waste, the Thames had become a cesspool whose stink was so bad that in 1858 Parliament was shut down. At that point, the authorities knew that they needed to act and a decades long project of creating underground sewers ensued.
The "Great Stink" was it was called would have been a terrifying event for Londoners of the time. There was a widespread belief, dating back to the medieval period, that disease travelled with bad smells - miasmas - and so many Londoners would have felt a constant anxiety regarding the smell, fearing that it would pass on to them some vile disease. Interestingly, this same fear is not unknown to us today. Although we know now that "miasmas" don't carry disease, we do experience the terror and anxiety accompanying the global pandemic and the invisibile presence of germs. Like Victorian Londonders, we leave our homes with the needling anxiety that the disease we fear may be anywhere. Unfortunately for us, we don't have a terrible smell to warn us of its presence.
Source: https://www.museumoflondon.org.uk/discover/londons-past-air