Fundamentals Why concentration fluctuates

What does the mixing ratio (or the corresponding concentration depending on pressure and temperature) express at a given site and a given time It relates to positive (sources F+) and negative (sinks F ) volume-based (an air box or column with different spatial values x, y, and z Chapter 4.1.1) fluxes, as well as the resi- 

The state-of-the-art of gas analysis at the end of the nineteen s century is best described by Hempel (1913), a pioneer of gas analysis see also Haldane (1918). 

The following list should give an idea of which factors can influence the concentration value (note that we talk mainly on surface-near concentrations regarding the biosphere-atmosphere interaction)  

Transport. The turbulent and advective transport of air parcels (horizontally and vertically) is often the most important factor (mixing and dilution). Transport processes show another wide range of causes, but are mainly driven by density gradient (hence, T gradients). Thus, it is clear that characteristic daily and seasonal patterns can be observed (for example, the vertical down-mixing of air in the morning after a nocturnal inversion). 

Emission This flux from the earth s surface into the lower air layer is the most important input of trace substances, changing the mass and thereby the concentration. This flux shows strong variations with time, e. g. daily and seasonal concerning different biogenic processes (photosynthesis, respiration), as well as varying with other parameters (temperature, light, water), rush hour traffic (but there is also a weekly traffic cycle) and domestic fuel use (seasonal cycle). 

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