Determining the Effect of the Urban Air Pollutants HNO3 and O3 on Lichens

EPA Grant Number: F6F11240
Title: Determining the Effect of the Urban Air Pollutants HNO3 and O3 on Lichens
Investigators: Riddell, Jennifer A.
Institution: Arizona State University - Main Campus
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 2006 through September 1, 2009
Project Amount: $71,624
RFA: STAR Graduate Fellowships (2006) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Air Quality and Air Toxics , Ecological Indicators/Assessment/Restoration , Fellowship - Air Pollution


The decline of lichen populations in urban and industrialized areas has been well documented for more than one hundred years. Lichens have successfully been used as biomonitors of air pollution (especially SO2), and are a cheap and useful tool to evaluate air quality in areas without physical monitors. In the Los Angeles air basin, lichen populations have seriously declined and many species locally extant in the early 1900’s are no longer present in the surrounding mountains. The largest source of pollution in the L.A. air basin is the burning of fossil fuels for transportation, which results in the subsequent production of two pollutants of major concern, ozone (O3) and nitric acid (HNO3). Relatively few O3 investigations with lichens have been conducted and their results, while suggesting that the powerful oxidant is responsible for the observed biodiversity loss, have been equivocal. No investigations have been done to establish the toxicity of HNO3 to lichens, although it has been established as a phytotoxic pollutant.

I will examine the effects of HNO3 and O3 on two formerly abundant lichen species (Hypogymnia imshaugii and Ramalina menziesii) that have either disappeared from or declined in the L.A. air basin. In doing so I may be able to establish a determining factor in the decline or loss of almost half of the lichen species formerly found in the air basin, as well as provide a tool for other workers in the western U.S. in understanding the impacts of urban growth and air pollution on ecosystem health.


My proposed research has three components: transplants, fumigations, and lichen community surveys along pollution gradients. I will collect lichen thalli from healthy populations in areas of low pollutant concentration, and transplant them into their historic range in the L.A. air basin, monitoring their physiological responses over the high HNO3 and O3 deposition season. To establish the relative toxicity of each pollutant, transplanted thalli will be placed in fumigation chambers in a 2 x 2 factorial experiment where HNO3 and O3 are independent variables. I will also conduct surveys of the abundance of these lichen species along HNO3 and O3 gradients in their habitat ranges.

Expected Results:

I anticipate establishing whether each pollutant is individually toxic and to determine if they act synergistically or amelioratively in combination compared to controls. I expect to find that both pollutants are individually toxic to lichens, each with different physiological effects. Because HNO3 deposition is suspected of increasing O3 damage in plants, the two pollutants may also act synergistically on lichens as well.

Supplemental Keywords:

Air pollution, bioindicators, Hypogymnia imshaugii, lichens, nitric acid, ozone, Ramalina menziesii,, Scientific Discipline, Air, air toxics, Biochemistry, Environmental Monitoring, Ecology and Ecosystems, ambient air quality, ozone, Nitric oxide, lichens, environmental effects

Progress and Final Reports:

  • 2007
  • 2008
  • Final