I have a personal pollution monitor that has been recording higher levels of VOCs the last 18 hours or so and I'm trying to understand and consider the reasons for this. I live in a fairly busy city (250k population, 3k people per km2 so densely populated).
What are the more common reasons that could cause higher outdoor VOC readings in a city? The levels have been somewhere between 1 & 2ppm the last 18 hours, the four days prior it has been around 0.3ppm or less. Now it has subsided but seems to fluctuate between 0.3 and 1ppm.
Traffic, wood burners, open fires, factories, incinerators? Mould round the open window? Anything else? What are the most common sources of VOC pollution in a city?