How does pressure relate to chemical weathering?

Chemical weathering due to acid rain will be more likely near regions where fossil fuels are burned and that have low air pressure.  

To say that air pressure directly causes chemical weathering may be a bit of a reach. Weathering is the process that breaks apart rocks into smaller pieces. Chemical weathering breaks rocks apart by chemical means. As a result, the composition and molecular structure of rock may be changed.

Acid rain is one agent of chemical weathering. Acid rain is precipitation that is made acidic due to the presences of pollutants in the atmosphere. The burning of fossil fuels is one of the largest contributors of the production of acid rain. The carbon dioxide and sulfur that are emitted by the burning of fossil fuels dissolve into the water that condensates to form clouds. Thus, the precipitation formed by this water tends to be acidic.

Air rises near areas that have low air pressure. As air rises, it cools and condenses to form clouds and precipitation. Thus, the downfall of acid rain is more likely to occur near regions where fossil fuels are burned and have low air pressure. Thus, chemical weathering due to acid rain will be more likely to occur near regions where fossil fuels are burned and have low air pressure.