Final Report Summary - LAMUNIO (LAboratory and Modelling studies to UNderstand Isoprene Oxidation)
Recent field and laboratory evidence points towards a significant failure in our understanding of the atmospheric chemistry of isoprene in low NOx environments and notably its impact on OH radicals, significantly inhibiting our understanding of the atmosphere-biosphere-climate system. The multidisciplinary LAMUNIO project, included technique development, laboratory and chamber studies and modelling evaluation, it was a step forward to innovatively investigated isoprene chemistry. LAMUNIO contained three workpackages (WP):
• WP1) investigated interferences in the FAGE (Fluorescence Assay by Gaseous Expansion) technique for OH observation, looking particularly at compounds relevant to environments dominated by high biogenic emissions and low NOx where models and measurements do not agree.
• WP2) studied isoprene oxidation focusing particularly on OH and carbonyl measurement to validate proposed mechanisms.
• WP3) new techniques to study HO2 reactions relevant for low NOx chemistry.
The project provided underpinning laboratory studies to validate both measurement techniques and the proposed mechanisms that seek to explain the unexpected observations of high OH concentrations in environments dominated by the oxidation of isoprene in low NOx conditions. OH concentrations control the oxidative capacity of the atmosphere influencing important local (air quality) and global (methane concentrations and hence radiative forcing) issues. LAMUNIO provided world class research and training opportunities and the proposed work was facilitated by the unique breadth of knowledge and infrastructure available at the University of Leeds.
Results released to date by LAMUNIO comprise further developments of the FAGE technique with a focus on developing alternative calibration methods for OH and HO2 channels. For the first time the FAGE methodology has been directly calibrated over a wide range of temperature (273 K-343 K) and air pressure (450 mbar-1000 mbar), helping to validate not only laboratory studies, but also field measurements taken over a wide range of conditions on aircraft platforms. These results not only extended the temperature and pressure range using the traditional calibration method of water photolysis but also added new interesting way of calibration using kinetic approach with FAGE connected with HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry) chamber.
LAMUNIO added significant contributions to an on-going project where FAGE instrument and other HIRAC facilities (e.g. FTIR and GC) have been used to evaluate the branching ratio for the HO2 + acetyl peroxy (CH3C(O)O2) reaction. The link with LAMUNIO objectives arises since CH3C(O)O2 is of particular importance to the tropospheric chemistry as it is formed from the oxidation and photolysis of several VOCs, especially isoprene, with high impact for low NOx environments. This study provided the first direct observation of products from each of the three reaction channels in the CH3C(O)O2 + HO2 reaction significantly reducing the uncertainties in the measured branching ratios.
The reaction of isoprene with O3 leads to the formation of stabilized Criegee intermediates (SCIs). This reaction has been intensively studied during LAMUNIO. The SCI molecules undergo dissociation to form OH radicals or undergo other oxidation processes. Results on the study of temperature dependent formation yields of methacrolein (MACR), methyl vinyl ketone (MVK) and formaldehyde (HCHO) from ozonolysis of isoprene (ISOP) in the presence of OH scavenger show virtually no variation of the product formation yields over the range of the temperature investigated (273 K – 343 K). The effects of OH scavengers on the product formation yields have also been investigated. Preliminary results on the temperature dependent radical formation yields (OH and HO2) from the isoprene ozonolysis have been also obtained during LAMUNIO and analysis and modelling of these data are now in progress.
During LAMUNIO a few additional kinetic studies have been performed in order to provide data for the alternative calibration method for OH detection via FAGE. These studies include an extensive temperature dependent kinetic study to determine the rate coefficients for the reaction of a series of alkyl cyclohexanes with OH/Cl radicals over a wide range of temperature (273 K-343 K) and work on Cl atom reactions with ketones.
All these results are subjects of scientific publications which have been already released to the scientific community or are in progress to further communications.
• WP1) investigated interferences in the FAGE (Fluorescence Assay by Gaseous Expansion) technique for OH observation, looking particularly at compounds relevant to environments dominated by high biogenic emissions and low NOx where models and measurements do not agree.
• WP2) studied isoprene oxidation focusing particularly on OH and carbonyl measurement to validate proposed mechanisms.
• WP3) new techniques to study HO2 reactions relevant for low NOx chemistry.
The project provided underpinning laboratory studies to validate both measurement techniques and the proposed mechanisms that seek to explain the unexpected observations of high OH concentrations in environments dominated by the oxidation of isoprene in low NOx conditions. OH concentrations control the oxidative capacity of the atmosphere influencing important local (air quality) and global (methane concentrations and hence radiative forcing) issues. LAMUNIO provided world class research and training opportunities and the proposed work was facilitated by the unique breadth of knowledge and infrastructure available at the University of Leeds.
Results released to date by LAMUNIO comprise further developments of the FAGE technique with a focus on developing alternative calibration methods for OH and HO2 channels. For the first time the FAGE methodology has been directly calibrated over a wide range of temperature (273 K-343 K) and air pressure (450 mbar-1000 mbar), helping to validate not only laboratory studies, but also field measurements taken over a wide range of conditions on aircraft platforms. These results not only extended the temperature and pressure range using the traditional calibration method of water photolysis but also added new interesting way of calibration using kinetic approach with FAGE connected with HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry) chamber.
LAMUNIO added significant contributions to an on-going project where FAGE instrument and other HIRAC facilities (e.g. FTIR and GC) have been used to evaluate the branching ratio for the HO2 + acetyl peroxy (CH3C(O)O2) reaction. The link with LAMUNIO objectives arises since CH3C(O)O2 is of particular importance to the tropospheric chemistry as it is formed from the oxidation and photolysis of several VOCs, especially isoprene, with high impact for low NOx environments. This study provided the first direct observation of products from each of the three reaction channels in the CH3C(O)O2 + HO2 reaction significantly reducing the uncertainties in the measured branching ratios.
The reaction of isoprene with O3 leads to the formation of stabilized Criegee intermediates (SCIs). This reaction has been intensively studied during LAMUNIO. The SCI molecules undergo dissociation to form OH radicals or undergo other oxidation processes. Results on the study of temperature dependent formation yields of methacrolein (MACR), methyl vinyl ketone (MVK) and formaldehyde (HCHO) from ozonolysis of isoprene (ISOP) in the presence of OH scavenger show virtually no variation of the product formation yields over the range of the temperature investigated (273 K – 343 K). The effects of OH scavengers on the product formation yields have also been investigated. Preliminary results on the temperature dependent radical formation yields (OH and HO2) from the isoprene ozonolysis have been also obtained during LAMUNIO and analysis and modelling of these data are now in progress.
During LAMUNIO a few additional kinetic studies have been performed in order to provide data for the alternative calibration method for OH detection via FAGE. These studies include an extensive temperature dependent kinetic study to determine the rate coefficients for the reaction of a series of alkyl cyclohexanes with OH/Cl radicals over a wide range of temperature (273 K-343 K) and work on Cl atom reactions with ketones.
All these results are subjects of scientific publications which have been already released to the scientific community or are in progress to further communications.