[1] Horwell designed passive samplers to simultaneously measure gas emissions around the town, collecting information on hydrogen sulphide exposures and providing advice to public health experts.

[1] She earned her doctorate at the University of Bristol, where she worked with Robert Stephen John Sparks supported by the Natural Environment Research Council.

[5][6] She has remained the director of the IVHHN, and has since co-created the Hawaii Interagency Vog dashboard to provide information about volcanic smog to the general public.

Horwell studies the health hazards of mineral dusts, and ways to support communities to protect themselves from inhaling particulate air pollution.

She created the Health Interventions in Volcanic Eruptions (HIVE) Consortium project (funded by ELRHA) to collect evidence on respiratory protection for communities.

[15] She investigated the effectiveness of facemasks distributed by agencies during volcanic eruptions, looking to identify whether or not they could adequately filter fine-grained particles, as well as to understand the behavioural reasons why some communities may or may not wear masks, through collaborations with a range of social scientists.

[16] A summary of the project was published as a Supplement of the Pan American Health Organization's Disasters bulletin[17] which is distributed globally to more than 25,000 people.