Secrets of Vivergy Calculations Unveiled (Part 2)

(This is part 2 of 3 of a new series which will describe how to do your own air pollution to time spent in a car with a smoker calculations)

Here at Vivergy, we go out of our way to share what we know about air pollution, and help others understand how they might be able to better connect to such a complex scientific topic. We have really pushed to find ways to connect the data to each and every person across the United States, and avoid the trap of discussing the science in ways that are difficult to comprehend. We convey air pollution in three separate ways on the Vivergy platform: number of cigarettes inhaled per year, months of the year living with a smoker, and time spent in a sealed car with a smoker. Today, we want to let you know how to do your very own air pollution to time spent in a sealed car with a smoker calculation. Using these methods, you can convert any air pollution data measured in fine particulate matter (PM2.5). If you want to learn how to convert PM2.5 numbers to cigarettes, you can check out our post last week!

In order to compare the two, we make a fundamental assumption that the particulate matter in air pollution has the same makeup as the particulate matter in cigarettes. Fine particulate matter is a general class of pollutant that encompasses any airborne particle less than 2.5 micrometers in diameter. It is a standard measure of air pollution due to its harmful nature and its general application across all air systems. The smoke that one inhales when smoking a cigarette also falls under this class of particulate.

In order to convert time in a car with smoker to daily exposure, we must consider the following factors: length of time the person was in the car, how many cigarettes were smoked, amount of PM2.5 in the car and the level of air circulation in the car. Fortunately, Ott et al. have published a study on these factors. The formula goes:

Mean daily exposure to PM2.5= Average PM2.5 levels in car * (Minutes spent in car with smoker/minutes per day)

Average PM2.5 in the car is a constant. Assume the conditions that the car is going 20 mph, with all windows closed, air conditioning on regular levels, and one cigarette is smoked over 15 minutes. This leaves us with the following results:

529 ug/m3 (avg levels in car) * (15min/1440 min per day) = 5.5 ug/m3 of PM2.5 exposure per day.

Great! So now let’s work it backwards. What if outdoor air pollution averages 11 micrograms/m3 over the course of the day?

11 ug/m3= 529 ug/m3 (avg levels in car) * (X min/1440 min per day)

Since 11 is 2 times 5.5, X = 30 minutes. A day that averages 11 ug/m3 of PM2.5 is like spending half an hour in a sealed car with a smoker (assuming the car is going 20mph and AC is on).

Try it out yourself! Plug in today’s air pollution in your area, and see how it relates to time spent in a car with a smoker. Want to do something about it? Join Vivergy.

-The Vivergy Team


Ott WR, Klepeis NE, and Switzer P. (2007) Air Change Rates of Motor Vehicles and In-Vehicle Pollutant Concentrations from Secondhand Smoke. Journal of Exposure Analysis and Environmental Epidemiology. In Press.