2013 Progress Report: Assessing anthropogenic impact on secondary pollutant formation in the South Eastern US via airborne formaldehyde measurementsEPA Grant Number: R835406
Title: Assessing anthropogenic impact on secondary pollutant formation in the South Eastern US via airborne formaldehyde measurements
Investigators: Keutsch, Frank N
Institution: University of Wisconsin - Madison
EPA Project Officer: Hunt, Sherri
Project Period: April 1, 2013 through March 31, 2015 (Extended to March 31, 2016)
Project Period Covered by this Report: April 1, 2013 through March 31,2014
Project Amount: $194,183
RFA: Anthropogenic Influences on Organic Aerosol Formation and Regional Climate Implications (2012) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Global Climate Change , Climate Change , Air
The primary objective of the proposed work is to improve our mechanistic understanding of the anthropogenic influence on processes transforming primary emissions into secondary pollutants, especially ozone and secondary organic aerosol (SOA), and to constrain the temporal and spatial scales of this anthropogenic impact in the South Eastern United States. Specifically, airborne measurements of formaldehyde, in conjunction with a full suite of chemical and meteorological observations, will be used to evaluate the impact of anthropogenic volatile organic carbon (VOC) and nitrogen oxide (NOx) emissions on ozone and SOA production efficiency at the urban-rural interface. Analysis will focus on quantifying the degree of fragmentation versus functionalization, and the related extent of chain terminating reactions during the photochemical lifecycle of biogenic and anthropogenic VOCs. These factors determine the relative ozone productions rates and mass of reactive carbon in the gas and condensed phases. We will evaluate how synergistic and competitive mechanisms interact to influence SOA loadings and optical properties. Formaldehyde measurements will also enable improved isoprene emission models that can then be used as a reference for isoprene inferred from formaldehyde via satellite retrievals, which are critical to regional models of air quality.
In year 1, training of key personnel with the formaldehyde instrument and integration of the instrument on the NOAA P-3 aircraft were completed. This was followed by successful formaldehyde measurements on the NOAA P-3 as part of the Southeast Nexus (SENEX) component of the Southeast Atmosphere (SAS) Study during which the instrument performed extremely well for all flights. The instrument was deintegrated and data were submitted to the official data archive.
After the measurement phase, focus shifted to analysis of the formaldehyde measurements within the context of improving the understanding of anthropogenic influence on secondary pollutant formation in the South Eastern United States. Atmospheric oxidation of VOCs is directly coupled to the formation of secondary pollutants such as ozone and secondary organic aerosol. These oxidation processes also form formaldehyde and allow the use of formaldehyde as a down-stream test of how well VOC oxidation is represented in models. The different P-3 flight patterns provide the opportunity to conduct a number of different studies, such as investigation of the chemistry within plumes and contrasting urban and rural regimes of secondary pollutant formation.
Preliminary results of a study comparing photochemical formaldehyde production in power plant plumes in both rural and urban areas suggest that the model being used is missing formaldehyde sources. This finding is indicative of missing VOC oxidation, which, if correct, directly reflects missing secondary pollutant production. In a second study we have been contrasting formaldehyde production in regions with large and small influence from anthropogenic NOx emissions. Our preliminary results suggest that formaldehyde concentrations increase with increasing NOx but biogenic isoprene emissions also are a very strong driver of formaldehyde. Of particular interest is the effect of the anthropogenic NOx on formaldehyde in rural areas with high isoprene emissions.
The focus of year 2 will be completion of the detailed analysis of anthropogenic influence on secondary pollutant formation in the South Eastern United States using the successfully obtained formaldehyde as well as other chemical and meteorological observations in conjunction with models.