Particulate air pollution is a constantly growing problem in urban areas. The particulate matter present in pollution events contains often toxic or health impacting elements and is responsible for low visibility, might be triggering respiratory diseases like asthma, and can play an important role in formation or duration of smog events. To characterize particulate pollution and pollution patterns in a highly industrialized coastal city like Chicago, the Land-lake Breeze Effects study was performed during July/August 2002 and June/July 2003. Aerosol filter samples for determination of trace elements, ionic compounds and organic species were collected before and during the lake breeze. Sampling took place at Loyola University Chicago Air Station (LUCAS, approx. 60m above ground and 250m away from Lake Michigan) with a temporal resolution of 1.5hours and 1 hour for trace element aerosol samples, respectively. In addition to atmospheric aerosols, non-methane hydrocarbons (NMHCs) were collected and reactive trace gases monitored. An automated weather station recorded the major meteorological parameter during the length of the study on a continuous basis. The particulate samples were analyzed by total reflection X-ray fluorescence after digestion of the filter matrix to quantify the elemental concentration.

Three different situations could be distinguished based on wind patterns recorded: a lake breeze occurs, characterized by a wind shift towards the east during the late morning; a constant wind direction was present throughout the collection period; and a change in wind directions not related to the lake breeze i.e. not from the east, was measured. Results indicate that some elements, notably sulfur, experience different concentrations before and during the lake breeze but not on reference days. We think that this is related to photochemical reactions happening inside the air parcel residing above Lake Michigan, transported by westerly wind (land breeze) in the morning or during the night onto the lake. Pollutants trapped in this parcel are exposed to intense sunlight in summer and are able to react with each other to form secondary species such as sulfate. These results suggest that a lake breeze pattern like occurring in Chicago could have major implications for coastal environments with respect to human health. It might also alter local radiative properties of the aerosol since the processed particulates are often smaller in size, differently composed and more reactive as the non-processed ones. In order to solidify our findings, future investigations will include the characterization of secondary organic compounds besides the trace elements before and during the lake breeze.