Is some smoke alkaline when mixed with water?

AIUI, acid rain is only when some smoke compounds - industrial chemicals - get into rain, but otherwise smoke (like that from wood/campfire) should make for alkaline water when it touches water, right? (Because ashes normally mix with water to make lye)

The majority of acid rain comes from nitrous oxides and sulfur dioxide, which combine with moisture in the air to form nitric acid and sulfuric acid. A lot of it comes from industry and power generation. Coal in the eastern U.S. in particular contains a lot of sulfur. At the power plant I used to work at (several decades ago) we mixed cheaper eastern high sulfur coal with more expensive low sulfur western coal, and combined that with scrubbers to keep the plant’s emissions under EPA limits. Nitrous oxides are also common in car and truck exhausts, which is why we have catalytic converters (they convert unburned hydrocarbons into carbon dioxide and nitrous oxides into nitrogen and oxygen).

Somewhat surprisingly to some, there’s a lot of different things in wood smoke. While the ash that remains is alkaline, a lot of the combustion products are not. Smoke contains carbon dioxide and carbon monoxide, nitrous oxides, sulfur dioxide, aldehydes, dioxins, unburned hydrocarbons, and all kinds of stuff. I’m a little fuzzy on the chemistry, but I think the acidic substances produced (nitric acid from nitrous oxides, carbonic acid from carbon dioxide, sulfuric acid from sulfur dioxide, etc) will end up producing more of an effect on the pH of the rain than the alkaline chemicals produce.

But to answer your question, yes, some of the products in smoke will produce alkaline rain. IIRC though, they’ll be outnumbered by the amount of acid rain that is also produced.

You can definitely have alkaline rain though. It is most commonly produced from industrial processes. Calcium carbonate (lime) has a lot of uses, for example. Mineral dust, like that from gypsum plants or plants that crush lime for construction material use, contributes significantly to alkaline rain.

Weirdly, acid rain often ends up causing alkaline problems in streams and rivers, and the reason for that is that the acid ends up dissolving lime and other alkaline substances, which end up in local streams, rivers, and lakes.

Summarizing what engineer_comp_geek: said. The carbon particles in smoke aren’t acidic or alkaline. Volatile compounds in industrial exhaust can be acidic when dissolved in water, wood ashes can be alkaline when dissolved in water, but neither of those are defined as smoke – they’re just, kinda, nearby, as it were. You’re on a fools errand, if you try to find the exact acid in coal, or the exact alkali in wood, even if the source is there.

This is a non-sequitur because ashes are what doesn’t go up in smoke.

It should be noted here that “smoke” doesn’t mean “the gases that are produced by combustion”. What’s usually called “smoke” is in fact solid, tiny specks of material small enough to easily get swept up in air currents. So yes, smoke will, to at least some degree, be composed of the same substances as ash (though ash will disproportionately contain the more-dense substances, while smoke will disproportionately contain the less-dense substances).

The sulfur and nitrogen oxides that eventually lead to acid rain, however, are not solids, but completely gaseous.

While a very good post, it’s relevance to the OP is not very apparent.

Coal power plants are designed for complete combustion of coal and produce very little smoke. The two main things done for complete combustion are : 1. The coal is pulverized I.e. it’s ground to the consistency of baby powder. 2. The air to coal ratio is carefully controlled during combustion to about 15% excess ensuring total combustion. In addition there are scrubbers to remove SOx and ESPs (Electrical Static Precipitators ) to remove fly ash.

Back to the OP:
Smoke as you commonly see while burning wood or other biomass is undergoing incomplete combustion I.e. it’s not hot enough or it doesn’t have enough oxygen. When this happens, water and other volatile components vaporize and the vapor appears as smoke. Most volatile matter are either neutral or acidic, so smoke mixed with water will be acidic.

I have skipped technical chemistry terms, but can provide more details if you are interested.

And for the record: Fossil fuels have carbon and the result of combustion is CO2. Fossil fuels have sulfur and the result of combustion is SOx. Similarly fossil fuels have Mineral matter and the result of combustion is **ASH **:slight_smile: