# Smoking Multiple Cigarettes in a Home

The two main causes for the decrease in the secondhand smoke (SHS) particle concentration in a room with time – fresh air filtration through gaps and cracks and removal of particles due to deposition on surfaces – cause the particle concentration in the room to decrease with time, but the decrease for each cigarette occurs very slowly. Often cigarettes are smoked in a sequence, one after another. Each new cigarette adds to the pollution lingering from the previous cigarette. When this happens, the concentration from the first cigarette does not have enough time to drop appreciably before the second cigarette begins, and the overall concentrations in the room can remain high for long periods or can even increase over time.

Several studies of smoking in homes show high intensity SHS particulate pollution in rooms where smoking of one or more cigarettes takes place, and substantial peak and average levels in separate rooms. Particle levels from a single cigarette can persist at relatively high levels above 50 μg/m$^3$ for several hours.

For example, the top 5 panels of the figure above show simulated real-time SHS particle levels in the different zones of a typical house -- with labels giving the 24-hour average level (Source: Klepeis & Nazaroff, 2006$^{12}$). Cigarette activity, depicted by vertical bars in the bottom panel, leads to peaks in particle concentration in a given room as high as 300 μg/m$^3$. Peak particle levels reach 100-200 μg/m$^3$ in adjacent rooms to where smoking occurs, indicating that levels measured in any room of the house reflect elevated pollutant levels in other rooms. Average levels in adjacent rooms are also elevated. The 24-hour average particle levels of 35-51 μg/m$^3$ in rooms with the least smoking (bedroom, hallway) are about 50% to 90% of the average in rooms with the most smoking (kitchen, living room).

Note that in the example shown above, the 24-hour average particle concentration due to smoking equals or exceeds 35 μg/m$^3$, which is the 24-hour USEPA ambient air standard, for every room in the house except the bathroom.