Can a pH be negative?
The pH is calculated from an equation pH = -log([H+}, where [H+] represent the hydrogen (or hydronium) ion concentration in an aqueous solution, expressed in the concentration unit Molarity (M). Mathematically, the base 10 logarithm of 1 is zero. Thus, any acid concentration greater than 1M will have a negative pH. Consider the 12 M hydrochloric acid (HCl) in your school's lab. It has a pH = -log(12) = -(1.07) = -1.07. Note that log(12) is positive, and the negative sign in the equation makes the calculated pH negative. A general rule of thumb is that the pH of most substances commonly found in nature lies between 0 and 14. Hopefully, you won't encounter naturally occurring 12 M HCl in this lifetime!
How does the wind impact air pollution?
The wind may blow emitted pollutants horizontally, allowing mixing of chemicals, subsequent reactions, and potential population exposure to air pollutants. An important consideration, however, is the influence of winds in the vertical (up/down) direction. Days with significant upward air motion disperse pollutants away from the ground where people, animals, and plants would be exposed. Significant pollutant transport "aloft" may occur, with pollutants touching the surface far from their sources. Days with a downward moving (subsiding) airmass experience pollutant buildup near the sources. These days tend to be associated with high-pressure weather systems. The heat and sunlight may enhance chemical reactions forming secondary (non-emitted) air pollutants under such conditions. Air quality scientists pay particular attention to measuring and modeling meteorological parameters that help them infer vertical pollutant dispersion characteristics.
What is an octane rating?
First, octane, or specifically iso-octane, is a hydrocarbon molecule. It has eight (8) carbons in the most highly branched structure possible. (Check out a web search for "iso-octane Lewis structure"). It represents an ideal gasoline molecule, because it is easily ignitable, energy dense, and, importantly, exhibits chemical stability to prevent engine knocking (a bad thing). The octane rating for gasoline is based on comparing the combustion performance of a given fuel to that of iso-octane. So using pure iso-octane as an engine fuel would have an octane rating of 100. A fuel with an octane rating of 91 has 91% of the knocking resistance of pure iso-octane, It is quite possible for a fuel to have an octane rating higher than 100.