By Olivia Wrigley
Based at the University of York, UK, Nicola Carslaw is at the forefront of indoor air chemistry research. Despite the average human spending 90% of their time inside, the chemistry of indoor air pollution is still relatively unxplored. Carslaw furthers our knowledge by working with postdoc, Magdalena Kruza and PhD student, Zixu Wang, to use and develop her detailed chemical model with 31,000 lines of code, to simulate the chemistry of indoor air in exquisite detail.
Carslaw began her academic life at the University of East Anglia, Norwich, UK, where an atmospheric chemistry module during her undergraduate chemistry degree sparked her interest and lead to a masters in the field. After graduation, Carslaw joined the Technology and Environment Chemistry unit at the now defunct energy company National Power. The team she worked with flew aircrafts around the country collecting air samples, which Carslaw then analysed for hydrocarbons using gas chromatography. She soon realised that she missed academic life, and returned to the University of East Anglia to start a PhD on the reactions of the nitrate free-radical, an atmospheric oxidant.
In 1996, Carslaw moved to the University of Leeds, UK, to start a postdoc with Mike Pilling, who told her: “[this grant’s] for carrying out some modelling of emissions inventories, but you can do something interesting if you want!” It was in Leeds that Carslaw worked on the detailed chemical mechanisms that are now the backbone of her INdoor Detailed Chemical Model (INDCM).
In 2000, Carslaw joined the University of York as a lecturer in the Environment Department. Her first glimpse into the world of indoor chemistry came soon after her arrival, through a grant investigating air quality inside cars. An editorial Carslaw wrote in 2003 concerning this research caught the attention of one of the most highly respected scientists in the indoor air pollution field, Charles Weschler. He invited her to attend an indoor air meeting the following year, and Carslaw soon crossed the boundary into the indoor world. Carslaw describes the transition between indoor and outdoor chemistry as a “no-brainer”, drawn to a field wide-open to investigation and host to an extremely welcoming and inclusive set of peers.
Unusual in the world of academics, Carslaw worked part-time from 2002 to 2015 due to childcare commitments. Working part-time did not hold her back, however, her model continued to develop, and in 2009 she was promoted to senior lecturer and then to reader in 2014.
Carslaw’s involvement in the Alfred P Sloan Foundation-funded Chemistry of Indoor Environment (CIE) program began in 2015 in Lille, France, where she met Paula Olsiewski, the program director. In 2017, Carslaw was appointed co-lead of the CIE MOdelling Consortium for Chemistry of Indoor Environments (MOCCIE) project, together with Manabu Shiraiwa from the University of California, Irvine. This project brings together six different indoor air models whose abilities range from looking at reactions on the molecular scale, to movement of pollutants around buildings using computerised fluid dynamics.
Carslaw was recently awarded a second CIE grant to convert the 31,000 lines of code in her INDCM model into an open source model. The new model will be available in 2020, without a paywall and with a user-friendly interface – allowing both modellers and experimentalists to further develop her work. As Carslaw explains it, models and experiments make up a “two-way process”, experiments “validate, initialise and provide further insight” to model outputs, which in turn can highlight species and pathways that have not yet been measured experimentally.
Outside of the Sloan Foundation, Carslaw is leading the INDAIRPOLLNET (INDoor AIR POLLution NETwork) funded by COST (European Cooperation in Science and Technology). This network brings together ~100 scientists of various disciplines from 28 European countries, with the aim of bridging the gap between research and business to optimise indoor air quality in European buildings.
Kruza works alongside Carslaw, in her first postdoc position, focusing on incorporating particle-forming reactions into the INDCM. Kruza graduated with an undergraduate degree in environmental science in 2010 from the Warsaw University of Life Science, Poland. She then completed a “double-degree” masters in environmental science at the same Polish university and urban management at Wageningen University and Research in the Netherlands, graduating in 2012.
After a few years away from science, in 2014, Kruza joined the University of York, having seen an advertisement for the CAPACITIE (Cutting-edge Approaches for Pollution Assessment in Cities) PhD programme sponsored by Marie Skłodowska-Curie Actions. The programme brought together 12 PhD students of varying disciplines across the university each looking into various aspects of urban pollution. Kruza’s project entailed monitoring and modelling the impact of surface interactions on indoor air quality and then using the results to developing Carslaw’s model.
As part of her PhD, Kruza had the opportunity to intern at the US National Institute for Safety and Health (NIOSH) for 6 – weeks. There, Kruza carried out experiments simulating various cleaning conditions and their impact on indoor air chemistry. The resulting experimental data was later fed into Carslaw’s model. Kruza considers her experience at NIOSH to be a highly valuable part of her PhD as it allowed her to develop new skills and view her discipline from another perspective.
Since submitting her PhD earlier this year, Kruza has continued to work with Carslaw as a postdoc. Her current focus is to add information about gas to particle reactions seen during the degradation of volatile organic compounds into the model.
Unusually for a postdoc, Kruza works remotely from her home near London. Working from home has its perks, the luxury of choosing her own hours and the closeness to her husband. However, she admits it takes a lot of discipline to remain self-motivated, and although she might not miss the lengthy coffee breaks to distract her, Kruza finds that sometimes “you miss having other human beings around you!”
Wang is finishing his first year as a self-funded PhD student with Carslaw. He came to York from Shanghai, China, in 2014 to complete an undergraduate degree in environmental science. He says he opted to study in the UK to take advantage of our shorter 3-year undergraduate degree programmes; a comparable degree takes 4-5 years in China. Wang was attracted to indoor air pollution for his PhD due to the notoriously poor air quality in urban China and the fact that people spend so much time indoors.
As a self-funded student, Wang has more freedom to develop his project as he wishes compared to a student funded through a government or industry grant, for example. His project currently has two prongs. He uses a low-cost way of measuring NO2 indoors using a diffusion tube containing a filter on which NO2 in the air is passively collected typically over two weeks. Samples are then analysed using colorimetric spectroscopy to determine concentration of NO2 present. To test his kit, Wang has been measuring NO2 levels in the air inside five identical student apartments in York.
The second half of Wang’s PhD work measures the influence of different light sources on indoor air chemistry. Wang uses Carslaw’s model to investigate how the photolysis rate of NO2 varies between different intensities and types of light (such as halogen, LED, and fluorescent tubes).
Following his PhD, Wang says he plans to return to Shanghai and hopes to get either a research job or to work with the government there to help develop policies to improve China’s air quality.
 McDonald, B. C., de Gouw, J. A., Gilman, et al. Volatile chemical products emerging as largest petrochemical source of urban organic emissions. Atmospheric Chemistry. 2018;359:760-764.
 Carslaw, N. New Directions: Where next with indoor measurements? Atmospheric Environments. 2003;37:5645-5646.