Air pollution is the second most severe impact that the tourism sector has on the environment, after water pollution. The automobiles used for ground transportation has been principle source of the tourism-related air pollution. Automobiles have been known to emit by far the most carbon monoxide, nitrogen oxide, and volatile organic compounds in comparison to other transportation. It could be implied that the impact of automobiles (air and noise pollution, acreage for roads, gasoline stations) may be more significant than the impact of the visitors themselves. Tour buses have an impact on air quality as well. Another form of ground transportation that has grown since past decade is the recreational vehicle (RV) and off-road recreational vehicle (ORV) sector. Adverse impacts on vegetation in state parks have been attributed to automobile exhausts (Ruiz Sandoval, 1997).
Besides ground transportation, cruise industry has significant potential to affect air quality through engine emissions. Most marine fuels used in ships are residual fuels with higher concentrations of contaminants such as sulfur. Recent studies have suggested that ocean-going vessels have the potential to affect air quality in coastal regions, port areas, and heavily traveled trade routes where annual sulfur emissions from ships equals or exceeds land-based emissions (Zarate Lomeli et al., 1999).
Marine recreational vehicles do not emit carbon monoxide as much as automobiles, but they do emit significantly more of it than recreational land vehicles (such as off-road vehicles) and aircraft. Although aircraft contribute only a small amount to total air pollution, emissions from this source is increasing. Besides transportation, construction of tourism related infrastructure has numerous impacts on air quality. The dust and particulate matter generated from the construction of coastal tourism facilities and roads may cause stress in the marine environment and impact plants in sensitive ecological areas.