Visibility is impaired when fine particulate matter (or PM2.5) in the atmosphere scatters and absorbs light, thus creating haze. PM2.5 can foul the air as primary particulates or as secondary particulates formed from photochemical reactions and condensations of gas-phase precursors. Secondary particulates are especially serious in impairing visibility as these smaller pollutants can remain suspended in the atmosphere for longer periods and can be transported longer distances, thereby leading to visibility impairment on a regional scale. PM2.5 is difficult to quantify because its formation, transport and removal from the atmosphere is complex, making it difficult to know which pollutants should be controlled most effectively to improve visibility. But sophisticated air quality models may be the answer to our woes in this regard, helping to select the most effective strategies for reducing emissions, thereby improving air quality and visibility at the same time.