Advances in air quality research – current and emerging challenges
Authors: Sokhi Ranjeet S. , Moussiopoulos Nicolas , Baklanov Alexander , Bartzis John , Coll Isabelle , Finardi Sandro , Friedrich Rainer , Geels Camilla , Grönholm Tiia , Halenka Tomas , Ketzel Matthias , Maragkidou Androniki , Matthias Volker , Moldanova Jana , Ntziachristos Leonidas , Schäfer Klaus , Suppan Peter , Tsegas George , Carmichael Greg , Franco Vicente , Hanna Steve , Jalkanen Jukka-Pekka , Velders Guus J. M. , Kukkonen Jaakko 
Published: April 2022

Abstract. This review provides a community's perspective on air quality
research focusing mainly on developments over the past decade. The article
provides perspectives on current and future challenges as well as research
needs for selected key topics. While this paper is not an exhaustive review
of all research areas in the field of air quality, we have selected key
topics that we feel are important from air quality research and policy
perspectives. After providing a short historical overview, this review
focuses on improvements in characterizing sources and emissions of air
pollution, new air quality observations and instrumentation, advances in air
quality prediction and forecasting, understanding interactions of air
quality with meteorology and climate, exposure and health assessment, and
air quality management and policy. In conducting the review, specific
objectives were (i) to address current developments that push the boundaries
of air quality research forward, (ii) to highlight the emerging prominent
gaps of knowledge in air quality research, and (iii) to make recommendations to guide the direction for future research within the wider
community. This review also identifies areas of particular importance for
air quality policy. The original concept of this review was borne at the
International Conference on Air Quality 2020 (held online due to the COVID
19 restrictions during 18–26 May 2020), but the article incorporates a wider
landscape of research literature within the field of air quality science. On
air pollution emissions the review highlights, in particular, the need to
reduce uncertainties in emissions from diffuse sources, particulate matter
chemical components, shipping emissions, and the importance of considering
both indoor and outdoor sources. There is a growing need to have integrated
air pollution and related observations from both ground-based and remote
sensing instruments, including in particular those on satellites. The research
should also capitalize on the growing area of low-cost sensors, while
ensuring a quality of the measurements which are regulated by guidelines.
Connecting various physical scales in air quality modelling is still a
continual issue, with cities being affected by air pollution gradients at
local scales and by long-range transport. At the same time, one should allow
for the impacts from climate change on a longer timescale. Earth system
modelling offers considerable potential by providing a consistent framework
for treating scales and processes, especially where there are significant
feedbacks, such as those related to aerosols, chemistry, and meteorology.
Assessment of exposure to air pollution should consider the impacts of
both indoor and outdoor emissions, as well as application of more sophisticated,
dynamic modelling approaches to predict concentrations of air pollutants in
both environments. With particulate matter being one of the most important
pollutants for health, research is indicating the urgent need to understand,
in particular, the role of particle number and chemical components in terms
of health impact, which in turn requires improved emission inventories and
models for predicting high-resolution distributions of these metrics over
cities. The review also examines how air pollution management needs to
adapt to the above-mentioned new challenges and briefly considers the
implications from the COVID-19 pandemic for air quality. Finally, we provide recommendations for air quality research and support for policy.