Use of Lidar Backscatter to Determine the PBL Heights in

New York City, NY

Jia-Yeong Ku, Chris Hogrefe, Gopal SistlaNew York State Department of Environmental Conservation

Albany, NY 12233And

Shuki Chaw, Leona Charles, Barry GrossCity College of City University of New York

New York, NY 10031

Objective

• Analyze Lidar Backscatter to determine PBL Heights using Wavelet method

• Demonstrate the potential of applying Lidar Backscatter in the air quality forecast evaluation

Data

• Lidar measured backscatter signal

• PBL heights and aerosol extinction coefficients out of WRF/CMAQ air quality forecast system

Lidar System

• Lidar (Light Detection And Range) measures the intensity of backscattered light as a function of distance

• The primary contribution of scattering is from aerosol particles suspended in the air

Lidar Backscatter

R

T drRT

r eR

RPCRP 0

,2

20 ,

,

C: calibration constant

β: backscatter coefficient

α: extinction coefficient

CCNY Lidar Setup

Quanta_Ray HG-1Harmonic Generators

LICEL TR 40-160Photon Counter

0.1 – 50 HzRepetition rate

LICEL TR 40-160Data acquisition

3.5 ns at 1064 nm

3 ns at 532, 352 nm Pulse Duration

Hamamatsu

PMT: R758-10

PMT: R758-10

APD

Detectors

532 nm

355 nm

1064 nm

500 mJ at 1064 nm

250 mJ at 532 nm

200 mJ at 355 nm

Energy/pulse

70 “ (1778 mm)Focal length1064, 532, 355 nm Wavelength

Newtonian telescope

20 “ (50.8 mm)

Telescope Aperture

Q-Switched Nd: YAG

Infinity 40-100 Laser

Receiver Transmitter

Quanta_Ray HG-1Harmonic Generators

LICEL TR 40-160Photon Counter

0.1 – 50 HzRepetition rate

LICEL TR 40-160Data acquisition

3.5 ns at 1064 nm

3 ns at 532, 352 nm Pulse Duration

Hamamatsu

PMT: R758-10

PMT: R758-10

APD

Detectors

532 nm

355 nm

1064 nm

500 mJ at 1064 nm

250 mJ at 532 nm

200 mJ at 355 nm

Energy/pulse

70 “ (1778 mm)Focal length1064, 532, 355 nm Wavelength

Newtonian telescope

20 “ (50.8 mm)

Telescope Aperture

Q-Switched Nd: YAG

Infinity 40-100 Laser

Receiver Transmitter

Lidar data: 1064 nm channelTemporal resolution: 1 minuteVertical resolution: 37.5 m

WRF/CMAQ Forecast System

• Meteorology/Emission: Based on NECP/NWS 48-hr WRF forecasts initialized at 12:00 UTC and 2002/2004 emission inventory, processed with PREMAQ

• Photochemical Model: CMAQ (ver 4.51)

Horizontal resolution: 12 km

vertical resolution: 22 layers, lowest layer ~40 m• Study periods: July 31 – August 2, 2006

NWS Eta 12km 48hr Forecast Initialized at 12:00 UTC

NWS Eta-Post (vertical interpolation)

NWS Product Generator(horizontal interpolation)

NWS Eta for CMAQ22 sigma layer, 12 km,Lambert-Conformal

Location: National Weather Service (NWS)

EPA gets Eta for CMAQ to EPA NESC

EPA stores emission input files at EPA NESC

Location: EPA RTP Atmospheric Modeling Division National Environmental Supercomputing Center (NESC)

NYSDEC runs PREMAQ at EPA NESC to generate model-readymeteorology and emissions

NYSDEC brings PREMAQ output (model-ready emissions and meteorology) back to their Linux cluster

Location: NY State Department of Environmental Conservation (NYSDEC)

NYSDEC runs CMAQ using PREMAQ model-ready emissions and meteorology for near-realtime O3 and PM forecasts on NYSDEC Aspen Linux Cluster. Postprocessing finishes by 05:30 EDSTResearch Mode: Run alternate CMAQ version from 5.30 to 9.30 EDST

EPA gets NOAA AQ forecasting output (NE domain) and archives at EPA NESC

NWS CMAQ-Eta 12km O3 forecasts for Northeast (NE) domain

08:00

10:00

13:00

20:00

18:00

21:00

23:00

01:00

05:30

EDST

Modeling Domain

Analyze Lidar Backscatter for PBL Heights

• Boundary layer usually has much higher aerosol concentration than free troposphere above.

• The significant change in the backscatter across the top of the BL provides a means of determining PBL heights.

• Wavelet provides a scale-dependent approach to determine PBL height.

Wavelet Covariance Transform

W a ba

f z hz b

adz

zb

zt( , ) ( ) ( )

1

hz b

a

ba

z b

b z ba

elsew here

( )

:

:

:

12

12

0

The key of the wavelet analysis is the selection of an appropriatedilation (vertical scale).

Compare PBL heights of Lidar measured and Model predicted

• Lidar measures aerosol layers

• Model determines vertical mixing based on some meteorological parameters, such as temperature and wind field

Compare Lidar Backscatter and CMAQ Extinction Coefficient

• Hourly and vertical averaged Lidar Backscatter signal

• Hourly extinction coefficient of CMAQ outputs

• A qualitative comparison; both backscatter and extinction coefficient reflect the aerosol and humidity loading in the atmosphere

July 31, 2006

August 1, 2006

August 2, 2006

Summary• A wavelet technique is applied to analyze the

PBL height using lidar backscatter measured in New York City

• WRF/CMAQ forecast system keeps track the lidar measured PBL development well

• WRF/CMAQ forecast system predicted the vertical PM profile (in terms of extinction coefficient) resemble to the backscatter vertical profile under cloud free conditions

• Development in the areas that we can directly compare the aerosol optical products between Lidar and model.