Improved Photolytic Rate Measurements at PAMS SitesEPA Grant Number: R826772
Title: Improved Photolytic Rate Measurements at PAMS Sites
Investigators: Rodgers, Michael O. , Pearson, James R.
Institution: Georgia Institute of Technology
EPA Project Officer: Hahn, Intaek
Project Period: March 22, 1999 through March 21, 2001
Project Amount: $168,930
RFA: Air Pollution Chemistry and Physics (1998) RFA Text | Recipients Lists
Research Category: Air , Engineering and Environmental Chemistry
Description:We hypothesize the absence of reliable measurements of major UV photolytic rate coefficients has a significant and demonstrable effect on interpretive analysis of air quality field measurements regarding ozone and particulate matter chemistry. Our major research objectives are to develop, test and validate a system to make these photolytic measurements and to evaluate the influence of these measurements on photochemical models using field measurement data from PAMS sites.
Approach:Until recently, spectro-radiometer systems with sufficient spectral resolution to make accurate atmospheric photolytic rate measurements have been too large, costly and unstable to be considered for routine unattended operation at field measurement sites. At this time, however, continued improvements in large Charged-Coupled Device (CCD) detector arrays, ultraviolet optical fibers, and portable computers have made such a system practical for routine unattended operation. Here we propose to develop such a system and to test its operation at one or more active PAMS stations during the 1999 and 2000 ozone seasons. The system will be designed for unattended operation and will produce measurements of the photolytic rate for ozone j(O1D), nitrogen dioxide j(NO2), hydrogen peroxide j(H 2O2), nitric acid j(HNO3), nitrous acid j(HONO), formaldehyde (CH2O), methyl peroxide j(CH3OOH), methyl nitrate j(CH3ONO2) and other compounds of atmospheric interest using the spectrally-resolved radiometric method. To validate these measurements, the system will be compared to a dual coaxial actinometer system developed at Georgia Tech. These measurement will also be compared to model calculations based on the Georgia Tech Air Quality Laboratory two- and four-stream radiative transfer models and standard empirical models to more fully evaluate the strengths and weaknesses of this approach for implementation at PAMS and other field sites.
Expected Results:The primary results expected are in the development and testing of a system to accurately measure a variety of photolytic rate coefficients of atmospheric interest and analysis of the influence that these measurements have on air quality modeling results. The largest differences are expected under partly cloudy and/or early-morning/late-afternoon conditions where current methods have serious weaknesses.
Improvement in Risk Assessment or Risk Management: This capability should result in a significant improvement in our ability to effectively use future PAMS data for risk assessment and control strategy development.