Organic compounds are chemical species that are mainly composed of carbon and hydrogen with some functionality provided by other elements such as oxygen, nitrogen or sulfur. The organic species which are of the most significance for this work are those that exist primarily in the gas phase due to their low volatility.
VOCs play a major role in the chemistry of our atmosphere despite their presence at very low concentrations. VOCs are responsible for the oxidative photochemistry of our atmosphere leading to the formation of tropospheric ozone, which is toxic, and they also play a major role in the formation of secondary organic aerosols (SOA) in the atmosphere.
The sources of organic trace gases are varied and wide-ranging, and include driving, cooking, solid fuel burning and even breathing. There are many biogenic sources of VOCs as well as all plants and trees naturally produce organic compounds primarily highly reduced compounds such as isoprene and terpenes.
The aim of this project is to perform the most detailed analysis and measurements to date of volatile organic compounds in Ireland. These measurements will be performed using a state-of-the-art time-of-flight mass chemical ionisation mass spectrometer (ToF-CIMS). This instrument can detect species up to a limit of <10 parts per trillion for certain species making it one of the most sensitive techniques for VOC analysis. Source attribution of the detected VOCs will also be performed to classify the processes that are having the greatest impact on the concentrations of VOCs in the atmosphere.
This research is funded by the Irish Research Council through a Government of Ireland Scholarship and by the Environmental Protection Agency of Ireland.
Title: Sources, Fates and Impacts of Volatile Organic Compounds in Ireland
Fellow: Niall O’Sullivan
Supervisor: Prof. John Wenger
Grant Number: GOIPG/2017/1364
Start Date: 1st October 2017
Completion Date: 30th September 2021
Amount of Award: €96,000
VOCs play a significant role in the photochemical processes occurring in the troposphere which is the lowest layer of the Earth’s atmosphere. They are constantly oxidised by radicals, primarily the hydroxyl (OH) radical but they can also interact with nitrate (NO3) and chloride (Cl) radicals. Subsequent to these oxidation reactions, the oxidised VOC species can react with nitrogen monoxide (NO) yielding nitrogen dioxide (NO2) which is a direct precursor to the formation of tropospheric ozone, a known pollutant which is harmful to living organisms. VOCs can have other impacts on the atmosphere in addition to their photochemical reaction pathways. Certain organic trace gases can act as greenhouse gases and can also contribute to the formation of particles in the atmosphere when they have been oxidised.
VOCs are also important precursors to the formation of secondary organic aerosols (SOA) which are a major component of particulate matter, particularly particles with a diameter of 2.5 microns or less (PM2.5). Aerosols are liquid or solid particles which are suspended in the atmosphere and they have an important role in the chemistry of the atmosphere as well as having an impact on climate. These aerosols can absorb and scatter radiation depending on their chemical composition. They can also offer a surface for heterogeneous reactions in the atmosphere to occur.
The formation of SOA can occur when oxidised products from VOCs condense on particles which are already present in the atmosphere. This can occur when the oxidation species have volatilities which are low enough to allow them to condense onto the surface of particles as an equilibrium is established between the gas and particle phase.
Thus VOCs play a major role in both climate and human effects in the lower atmosphere. By monitoring the concentrations of VOCs and then performing source apportionment studies on these compounds, conclusions can be made regarding ambient air quality which in turn may lead to recommendations for legislation regarding VOCs.