Cameron McErlich

Airborne microplastics are a recently identified atmospheric aerosol species with potential air quality and climate impacts, yet they are not currently represented in global climate models. Here, we describe the addition of microplastics to the aerosol scheme of the UK Earth System Model (UKESM1.1): the Global Model of Aerosol Processes (GLOMAP). Microplastics are included as both fragments and fibres across a range of aerosol size modes, enabling interaction with existing aerosol processes such as ageing and wet and dry deposition. Simulated microplastics have higher concentrations over land, but can be transported into remote regions including Antarctica despite no assumed emissions from these regions. Lifetimes range between ∼17 d to ∼1 h, with smaller, hydrophilic microplastics having longer lifetimes. Microplastics are present throughout the troposphere, and the smallest particles are simulated to reach the lower stratosphere in small numbers. Dry deposition is the dominant microplastic removal pathway, but greater wet deposition occurs for smaller hydrophilic microplastic, due to interactions with clouds. Although microplastics currently contribute a minor fraction of the total aerosol burden, their concentration is expected to increase in future if plastic production continues to increase, and as existing plastic waste in the environment degrades to form new microplastic. Incorporating microplastics into UKESM1.1 is a key step toward quantifying their current atmospheric impact and offers a framework for simulating future emission scenarios for an assessment of their long term impacts on air quality and climate.

Airborne microplastics are a recently identified atmospheric aerosol species with potential air quality and climate impacts, yet they are not currently represented in global climate models. Here, we describe the addition of microplastics to the aerosol scheme of the UK Earth System Model (UKESM1.1): the Global Model of Aerosol Processes (GLOMAP). Microplastics are included as both fragments and fibres across a range of aerosol size modes, enabling interaction with existing aerosol processes such as ageing and wet and dry deposition. Simulated microplastics have higher concentrations over land, but can be transported into remote regions including Antarctica despite no assumed emissions from these regions. Lifetimes range between ~17 days to ~1 hour, with smaller, soluble microplastics having longer lifetimes. Microplastics are well-mixed throughout the troposphere, and the smallest particles are simulated to reach the lower stratosphere in small numbers. Dry deposition is the dominant microplastic removal pathway, but greater wet deposition occurs for smaller soluble microplastic, due to interactions with clouds. Although microplastics currently contribute a minor fraction of the total aerosol burden, their concentration is expected to increase in future if plastic production continues to increase, and as existing plastic waste in the environment degrades to form new microplastic. Incorporating microplastics into UKESM1.1 is a key step toward quantifying their current atmospheric impact and offers a framework for simulating future emission scenarios for an assessment of their long term impacts on air quality and climate.

Airborne microplastics are a recently identified atmospheric aerosol species with potential air quality and climate impacts, yet they are not currently represented in global climate models. Here, we describe the addition of microplastics to the aerosol scheme of the UK Earth System Model (UKESM1.1): the Global Model of Aerosol Processes (GLOMAP). Microplastics are included as both fragments and fibres across a range of aerosol size modes, enabling interaction with existing aerosol processes such as ageing and wet and dry deposition. Simulated microplastics have higher concentrations over land, but can be transported into remote regions including Antarctica despite no assumed emissions from these regions. Lifetimes range between ~17 days to ~1 hour, with smaller, soluble microplastics having longer lifetimes. Microplastics are well-mixed throughout the troposphere, and the smallest particles are simulated to reach the lower stratosphere in small numbers. Dry deposition is the dominant microplastic removal pathway, but greater wet deposition occurs for smaller soluble microplastic, due to interactions with clouds. Although microplastics currently contribute a minor fraction of the total aerosol burden, their concentration is expected to increase in future if plastic production continues to increase, and as existing plastic waste in the environment degrades to form new microplastic. Incorporating microplastics into UKESM1.1 is a key step toward quantifying their current atmospheric impact and offers a framework for simulating future emission scenarios for an assessment of their long term impacts on air quality and climate.

Airborne microplastics are a recently identified atmospheric aerosol species with potential air quality and climate impacts, yet they are not currently represented in global climate models. Here, we describe the addition of microplastics to the aerosol scheme of the UK Earth System Model (UKESM1.1): the Global Model of Aerosol Processes (GLOMAP). Microplastics are included as both fragments and fibres across a range of aerosol size modes, enabling interaction with existing aerosol processes such as ageing and wet and dry deposition. Simulated microplastics have higher concentrations over land, but can be transported into remote regions including Antarctica despite no assumed emissions from these regions. Lifetimes range between ~17 days to ~1 hour, with smaller, soluble microplastics having longer lifetimes. Microplastics are well-mixed throughout the troposphere, and the smallest particles are simulated to reach the lower stratosphere in small numbers. Dry deposition is the dominant microplastic removal pathway, but greater wet deposition occurs for smaller soluble microplastic, due to interactions with clouds. Although microplastics currently contribute a minor fraction of the total aerosol burden, their concentration is expected to increase in future if plastic production continues to increase, and as existing plastic waste in the environment degrades to form new microplastic. Incorporating microplastics into UKESM1.1 is a key step toward quantifying their current atmospheric impact and offers a framework for simulating future emission scenarios for an assessment of their long term impacts on air quality and climate.

Airborne microplastics are a recently identified atmospheric aerosol species with potential air quality and climate impacts, yet they are not currently represented in global climate models. Here, we describe the addition of microplastics to the aerosol scheme of the UK Earth System Model (UKESM1.1): the Global Model of Aerosol Processes (GLOMAP). Microplastics are included as both fragments and fibres across a range of aerosol size modes, enabling interaction with existing aerosol processes such as ageing and wet and dry deposition. Simulated microplastics have higher concentrations over land, but can be transported into remote regions including Antarctica despite no assumed emissions from these regions. Lifetimes range between ~17 days to ~1 hour, with smaller, soluble microplastics having longer lifetimes. Microplastics are well-mixed throughout the troposphere, and the smallest particles are simulated to reach the lower stratosphere in small numbers. Dry deposition is the dominant microplastic removal pathway, but greater wet deposition occurs for smaller soluble microplastic, due to interactions with clouds. Although microplastics currently contribute a minor fraction of the total aerosol burden, their concentration is expected to increase in future if plastic production continues to increase, and as existing plastic waste in the environment degrades to form new microplastic. Incorporating microplastics into UKESM1.1 is a key step toward quantifying their current atmospheric impact and offers a framework for simulating future emission scenarios for an assessment of their long term impacts on air quality and climate.

Airborne microplastics, an emerging class of anthropogenic aerosols, are small and lightweight, allowing them to remain suspended in the atmosphere for extended periods of time. Their detection in remote locations (such as Antarctica) and in high-altitude cloud water raises questions about their potential impacts on climate systems. As global climate models do not routinely include airborne microplastics as an aerosol species, the full consequences of microplastics on climate remain uncertain. To investigate these impacts, we have incorporated micro- and nanoplastics (MnP) as a new aerosol species within GLOMAP-mode, the aerosol scheme used in the United Kingdom Chemistry & Aerosols (UKCA) component model of the UK Earth System Model (UKESM). MnP have been implemented in GLOMAP-mode alongside the existing aerosol species of sulfate, black carbon, organic carbon, sea salt and dust. Microplastics can be emitted into UKESM as both fragments and fibres. MnP are added to the Aitken (5 – 50 nm), accumulation (50 - 500 nm), coarse (> 500 nm) and super-coarse (> 2500 nm) modes. Emissions are sourced from an observationally-derived dataset with global spatial coverage. MnP are initially emitted in insoluble modes but can transition to soluble modes through the accumulation of organic material on their surfaces, enabling them to act as CCN. Airborne microplastics in UKSEM transported and can be removed from the atmosphere by both dry and wet deposition processes. We present preliminary results using the new microplastics scheme, which has been run for both microplastics fragments and fibres. Our novel microplastic scheme is a significant advancement in modelling airborne microplastics and lays the groundwork for understanding their impact on climate and the wider Earth system.

Microplastics and nanoplastics are recognised as common airborne pollutants, capable of being transported over large distances and altering the radiative properties of the atmosphere, with implications for global climate. Work in recent years has provided new constraints on many aspects of the spatial and temporal distribution of airborne plastics and their physical and optical properties. Using these updated findings, we perform simulations with the HadGEM3-GA7.1 atmospheric model to investigate the sensitivity of the direct radiative effect of airborne microplastics to these factors. Our ERF estimates range from -0.89 to +0.63 mW m-2 assuming an average surface concentration of 1 MP particle per cubic meter. We show that the sign of the radiative forcing depends on the colour of microplastic particles, and that the abundance of nanoplastics has the strongest influence on the magnitude of their radiative effect, emphasising the importance of experimental work to constrain the micro- and nanoplastic size distribution.

Because they are small and lightweight, airborne microplastics can remain suspended in the atmosphere for long periods. Microplastics appear to be ubiquitous in the atmosphere, having been identified at numerous remote sites and as high as 3500 m above sea level. Previously it has been shown that airborne microplastics may contribute to climate change by absorbing and scattering light. A weak cooling effect was calculated for direct microplastic-radiation interactions, subject to large uncertainties. Recent studies have identified the presence of microplastics in cloud water collected at high altitudes, suggesting that microplastics may act as cloud condensation nuclei (CCN). However, laboratory studies indicate that microplastics act as ice-nucleating particles (INP). The consequences of microplastics seeding cloud formation on climate change are unknown, as global climate models do not routinely include airborne microplastics, which are essentially a new class of anthropogenic aerosol. We present plans and progress for the implementation and assessment of microplastics as an aerosol species within GLOMAP-mode, the aerosol scheme used in the United Kingdom Chemistry & Aerosols (UKCA) component model of the UK Earth System Model (UKESM1.1). We aim to model microplastic-cloud interactions and their effect on climate so that together with microplastic-radiation interactions, the full effects of airborne microplastics on climate can be accounted for.

Extratropical cyclones are the primary source of precipitation in the mid-latitudes. The physical mechanisms that drive cyclones are well understood, and a variety of studies have demonstrated strong relationships between cloud structures and cyclone dynamics. However, past research has focused on simplistic cloud categorizations, which lack spatial and textural information that is included in more sophisticated classification schemes. Unsupervised deep learning approaches may have significant advantages over these past methods, allowing them to discover previously unidentified cloud information in large datasets. One such approach is the rotation-invariant cloud clustering (RICC), which combines a dimensionality reduction deep learning technique with rotation-invariant clustering of input cloud images. We employ the RICC, along with two established cloud clusters, to investigate the relationship between extratropical cyclones and horizontal cloud distributions. We focus on comparing these different sets of clusters to each other. First the spatial distributions and the physical properties of the identified cloud types are examined around cyclones and the results corresponding to each classification are compared in detail. Then the similarities of these distributions are quantified using structural similarity. Additionally, the evolution of spatial distributions of cloud over the lifetime of cyclones is compared between the different classifications. Interestingly, we identify the same broad physical developments in all sets of clusters. Notably, identified differences are likely due to differences in measurement processes and resolutions of the corresponding datasets.

ERA5 reanalysis output is compared to WindSat polarimetric microwave radiometer measurements for Southern Hemisphere midlatitude to high‐latitude cyclones between 2003 and 2019. WindSat provides independent measures of low‐level wind speed, total column water vapor (TCWV), cloud liquid water (CLW), and precipitation, which are not assimilated into ERA5. We implement a tracking scheme to identify cyclone centers, before using cyclone composites to match concurrent data in ERA5 and WindSat. We find ERA5 and WindSat show comparable spatial structures for all variables, although their distributions show poorer agreement for CLW and precipitation. Compared to WindSat, ERA5 underestimates TCWV by up to 5% and CLW by up to 40%. ERA5 underestimates precipitation in the warm sector by up to 15%, but overestimates in the cold sector by up to 60%. Similar biases in ERA5 are seen compared to Advanced Microwave Scanning Radiometer for EOS (AMSR‐E) data, even though AMSR‐E radiances are assimilated into ERA5. Comparing ERA5 and WindSat across the cyclone lifecycle, strong spatial correlation is seen as the cyclone deepens and reaches peak intensity, before slightly declining as the cyclone decays. In the cold sector ERA5 shows an underestimation of CLW, yet overestimates precipitation at all lifecycle stages. However, in the warm sector precipitation is underestimated. This potentially suggests biases within the ERA5 parameterizations of cloud and precipitation causing a disconnect between the two. Despite this, ERA5 shows strong correlation with WindSat and determines cyclone structure well across the cyclone lifecycle, showing its value for use in cyclone compositing analysis.