Nucleation and ageing of aerosol particles generated in the reactions of ozone with selected terpenes

Lead Research Organisation: University of Reading
Department Name: Chemistry

Abstract

In this proposal, experiments are described that aim to significantly improve our understanding of the role of the ozonolysis of terpenes (naturally emitted organic compounds) in the production and ageing of secondary organic aerosol (SOA) in the Earth's atmosphere. SOA consists of particles that are generated when terpenes and other compounds react in the atmosphere. It is visible as the haze generated in photochemical smog episodes, and has implications for health because the size of the particles is such that they are easily inhaled and lodge in the lungs. Furthermore SOA impacts on cloud formation, and so has significant implications for climate change. Experiments will be carried out using a static reaction chamber and flow reactor that will be interfaced with Scanning Mobility Particle Sizers, which are instruments that allow particle numbers and size distributions to be determined. The characterisation of particles will be performed as a function of time and reaction conditions, and where possible will be mapped against related experiments examining the chemical composition of the aerosol. In this way we will be able to obtain information about how the chemical components impact on aerosol formation (nucleation) and yield. In addition, the static chamber and flow reactor will be interfaced to an acoustic particle levitator. This is a novel technique that allows single seed particles to be suspended under conditions close to those that pertain in the atmosphere. The seed particle will become coated in SOA and we can examine it using a special microscope (Raman) that allows us not only to determine the size, but also to gain information about the chemical composition of the coated particle. We can then examine the ageing of aerosol in the presence of ozone and dinitrogen pentoxide, which are important oxidants in the atmosphere. The experiments will provide information on: the identity of the nucleation species; its mechanism of formation; and the ageing process. The results of the study will provide vital information that will inform atmospheric chemistry models.
 
Description Key findings have been generated in two areas: acoustic levitation of particles and the generation of particles in the ozonolysis of alpha-pinene and related compounds.

For the levitated particle experiments, there have been very significant difficulties associated with unexpected product formation in the absence of a key reactant. The results can at least partially be explained by the formation of radicals in the ultrasonic trap that suspends the particles. Although products in the presence of ozone can be detected, it is very difficult to seperate this process from the interference, and it creates some difficulty in understanding the reactive processes.

Experiments observing the generation of particles from the ozonolysis of alpha-pinene and two of its derivatives indicate that the very initial step in the process has little impact on the physical constitution of the particles (although does have an impact on the chemical products, as known form previous studies in our laboratory).
Exploitation Route The results show that special care must be taken when using acoustic levitation to study chemical processes, and future researchers must take this into consideration.

The results also show that some important chemical differences observed in the ozonolysis of alpha-pinene do not influence the physical nature of aerosol, indicating that the more general features of product structure are more important than the details in the generation of particles, an important observation for future researchers.
Sectors Environment
 
Description Engagement with school pupils and their teachers has helped in the public understanding of science and the environment.
First Year Of Impact 2010
Sector Education
Impact Types Societal
 
Description Arrangement with DEKATI to borrow a ELPI+ (Electrical Low Pressure Impactor) instrument. 
Organisation Dekati
Country Finland 
Sector Private 
PI Contribution We provided the infrastructure and staffing to use the ELPI+ instrument.
Collaborator Contribution Partner provided ELPI+ instrument
Impact No outputs yet, although a conference abstract has been submitted.
Start Year 2013
 
Description Visit of schools t oReading Chemistry Department 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Schools attended a workshop that covered a variety of chemical techniques, with an emphasis on their use in atmospheric chemistry
Year(s) Of Engagement Activity 2010