Spatial Variability of Atmospheric Transparency in the New York Metropolitan Area in SummerBeate Liepert, Autumn Anderson,and Natasha Ewart

Lamont-Doherty Earth Observatory of Columbia University, Palisades New York, Bronx High School of Science New York, New York (now Princeton University, New Jersey), High School for Environmental Studies New York, New York in collaboration with Carolyn Harris, Institute for Climate and Planets NASA Goddard Institute for Space Studies, New York, New York

IntroductionAtmospheric Transparency ~ Visibility ~ Air Quality

We present preliminary results of a fieldcampaign in Summer 2003 in New York City,where we used a handhold remote sensinginstrument (Microtops) for atmospherictransparency measurements. The goal wasdetermining optical thickness of polluted air inthe City in contrast to suburban areas anddetermining whether satellite retrieved aerosoloptical thickness is representative for NewYork City.

The Research Team and Educational Outreach The Research Project was part of the Summer Institute ofClimate and Planets, NASA Goddard Institute for SpaceStudies' educational outreach program for High Schoolstudents in NYC.

Microtops sunphotometermeasures aerosol optical thickness (AOT) at five wavelengths(380nm, 500nm, 675nm, 936nm, 1020nm). Rayleigh scatteringcorrection; portable, computer & GPS interface, calculates AOT andwater vapor content instantaneously.

Left: Retrieved average aerosol optical thickness AOT (500nm) monthly mean and for June 2003.Right: Retrieved column water vapor content monthly mean and for July 2003 (Courtesy MODIS team).

Left: Atmospheric transparency is attenuated by aerosol particulates, the most visible form of airpollution. Sub-micron particles are effective light scatterers and in case of soot effective light absorbers.Aerosol particles can grow with increasing ambient water vapor and form cloud condensation nuclei ifhumidity is very high. These activated particles reduce visibility drastically (haze).

Circle Line Route:3h Boat tour from Pier 83 at 42nd Street on the Hudson River heading south aroundManhattan Island to Statute of Liberty, north on the East River, east on Harlem River andback south on the Hudson River to the pier.

– Hot, humid day, some haze.– Atmospheric transparency increases with increasing humidity. Highest AOT near

Downtown off the southern tip of Manhattan. Hudson River and northern tip of Manhattanlowest AOT even though water vapor content is high -> less polluted by aerosols.

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Aerosol Optical Thickness Variability New York City Profile

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General Weather from 6.16 to 7.22.2003:

NYC Columbia University Area (Urban):Mean Temp = 24.2C +/- 2.8CRelative Humidity rH = 68% +/- 13%Calculated AOT ~ 0.31 +/- 0.12AOT500 = 0.36 (Hudson) to 0.42 (Morningside

Park)

Lamont (Rural):Mean Temp = 23.0C +/-

2.5CrH = 70% +/- 12%Calculated AOT ~ 0.24 +/-

0.11

Columbia University: (Urban)AOT500 = 0.96, Vis = 9.0 kmTmax = 32.8 CrH = 59 %, WV = 2.4 cm

Lamont: (Rural)AOT500 = 0.79, Vis = 9.9

kmTmax = 31.0 CrH = 63 %, WV = 2.6 cm

June 27th 2003: Hot and hazy day:

Summary

Acknowledgments: This work was sponsored by a grant from the National Science Foundation Division of Atmospheric Sciences andNASA Goddard Institute for Space Studies. MODIS data are provided by the MODIS team at NASA Goddard Space Flight Center(www.gsfc nasa.gov/MODIS)

East - West Profile across Midtown Manhattan:Hudson River pier on 72nd St, east to Lincoln Center, east through Central Park, east on 60th St toRoosevelt Island in the East River, east into Queens.

– Measurements directly in crowded Midtown and on the Rivers. Hot, dry, cloudfree day, some Cudeveloping, aerosol layers visible.

– Dryest contitions and hence lowest AOT in the Park. AOT clearly lower on the Westside near HudsonRiver (note water vapor content as high as in Queens) -> Westside less polluted.

Urban versus Suburban Comparison:Routine measurements taken around Columbia University and at rural Lamont Observatoryand in suburban Ridgewood, New Jersey,15 miles northwest of Manhattan in .

– With stable weather conditions aerosol particles can accumulate in rural areas and causehigh AOTs.

– June 23th (clean day after rain): AOT_rural=0.34, AOT_urban = 0.42;– June 24th: AOT_rural=0.46, AOT_urban = 0.42

New York City Profile:Measurements from Long Beach, Long Island acrossthree boroughs of New York City to Lamont-DohertyEarth Observatory.

– Spatial Variability of the metropolitan area under clear& clean weather conditions (AOT_500 ~ 0.20)

– Brooklyn and Long Island more polluted.– Rivers lowest AOT -> "ventilation effect".– North of Manhattan, New Jersey and Hudson Valley

cleanest.

Atmospheric transparency measurements from New York City to rural Lamont-Doherty EarthObservatory (15 miles north of Manhattan) show distinct spatial patterns between June 16th and July22nd.–Aerosol optical thickness generally higher in urban compared to suburban areas by about 20 % during cleanconditions.–HAZE is optically thicker in the City.–Rivers have a cleaning effect through ventilation.–Hudson River can transport polluted air to rural area causing lower atmospheric transparency in rural areacompared to City.–Off the Southern tip of Manhattan and East of Manhattan urban pollution plume more visible.

MODIS image of the day

JamaicaBay East River Hudson

Satellites are able to detect lifted plumes of polluted air emitted from urban areas.With satellites, the global climatic effects of urban air pollution can be assessed.

Project