Unraveling the interaction of urban emission plumes and marine breezes involved in the formation of summertime coastal high ozone on Long Island

The New York City (NYC) urban region and locations downwind (i.e., Long Island) are currently characterized as one of the critical regions for studying ozone pollution with special emphasis on the interplay of the urban plume and marine breeze on warm summer days. We use the data from a new air quality monitoring site at the Long Island south shore to provide a contrast to the existing measurements along the north shore and middle of the island. We find different mechanisms for high ozone cases at the north shore vs. those resulting in high ozone at the south shore. The north shore high ozone cases mainly result from (1) a calm condition favoring high ozone formation over NYC urban regions and western Long Island, (2) a sea-breeze front originating from south Long Island diverting the high ozone plume to the north shore, and (3) the stagnation of the sea-breeze front over the Long Island north shore (and coastal Connecticut) for several hours. The cases with higher elevated ozone on the south shore are rarely reported due to the limited measurements and are highlighted in this study. They resulted from more varied wind flow patterns, but in each case involved westerly or southwesterly flow and polluted air transported to the site over the ocean in the late afternoon (around 17:00 local time). Different from the previous studies over other regions in the world where the high ozone area generally happened further inland following the sea breeze front movement, the narrow high ozone band mainly covering Long Island south coastal line can be more harmful to the clustered people enjoying the summer beach. This study highlights the necessity of setting up more air quality monitors sites along the Long Island south shore and provides guidance for other shore regions for focusing on the potential for narrow high ozone bands concentrated over near coastal areas.