Tinja Olenius

Atmospheric new-particle formation is a major source of aerosol particles that influence air quality, cloud properties, and climate. Understanding the molecular mechanisms governing the initial steps of particle formation is therefore essential for accurately representing aerosol formation and its climatic effects in atmospheric models. Zhang et al. (2026c) recently proposed that hydrogen-bond–driven self-assembly of neutral carboxylic acids is a spontaneous and ubiquitous atmospheric new-particle formation mechanism. If correct, this would represent a fundamental shift in the current understanding of atmospheric nucleation. In this comment, we show that the proposed nucleation mechanism is not adequately supported by the observations or theoretical analysis presented in Zhang et al. The reported particle-composition measurements lack sufficient validation to establish the proposed molecular composition of the smallest particles and do not directly constrain the molecular processes responsible for the earliest stages of particle formation. Furthermore, using the thermodynamic data reported by Zhang et al., we demonstrate that cluster evaporation overwhelmingly exceeds growth by molecular collisions, resulting in negligible particle-formation rates under the reported atmospheric conditions. These kinetic and thermodynamic analyses demonstrate that hydrogen-bond–driven clustering of neutral carboxylic acids cannot explain the reported observations and is unlikely to represent an atmospherically relevant new-particle formation mechanism.

Atmospheric new-particle formation is a major source of aerosol particles that influence air quality, cloud properties, and climate. Understanding the molecular mechanisms governing the initial steps of particle formation is therefore essential for accurately representing aerosol formation and its climatic effects in atmospheric models. Zhang et al. (2026c) recently proposed that hydrogen-bond–driven self-assembly of neutral carboxylic acids is a spontaneous and ubiquitous atmospheric new-particle formation mechanism. If correct, this would represent a fundamental shift in the current understanding of atmospheric nucleation. In this comment, we show that the proposed nucleation mechanism is not adequately supported by the observations or theoretical analysis presented in Zhang et al. The reported particle-composition measurements lack sufficient validation to establish the proposed molecular composition of the smallest particles and do not directly constrain the molecular processes responsible for the earliest stages of particle formation. Furthermore, using the thermodynamic data reported by Zhang et al., we demonstrate that cluster evaporation overwhelmingly exceeds growth by molecular collisions, resulting in negligible particle-formation rates under the reported atmospheric conditions. These kinetic and thermodynamic analyses demonstrate that hydrogen-bond–driven clustering of neutral carboxylic acids cannot explain the reported observations and is unlikely to represent an atmospherically relevant new-particle formation mechanism.

Atmospheric new-particle formation is a major source of aerosol particles that influence air quality, cloud properties, and climate. Understanding the molecular mechanisms governing the initial steps of particle formation is therefore essential for accurately representing aerosol formation and its climatic effects in atmospheric models. Zhang et al. (2026c) recently proposed that hydrogen-bond–driven self-assembly of neutral carboxylic acids is a spontaneous and ubiquitous atmospheric new-particle formation mechanism. If correct, this would represent a fundamental shift in the current understanding of atmospheric nucleation. In this comment, we show that the proposed nucleation mechanism is not adequately supported by the observations or theoretical analysis presented in Zhang et al. The reported particle-composition measurements lack sufficient validation to establish the proposed molecular composition of the smallest particles and do not directly constrain the molecular processes responsible for the earliest stages of particle formation. Furthermore, using the thermodynamic data reported by Zhang et al., we demonstrate that cluster evaporation overwhelmingly exceeds growth by molecular collisions, resulting in negligible particle-formation rates under the reported atmospheric conditions. These kinetic and thermodynamic analyses demonstrate that hydrogen-bond–driven clustering of neutral carboxylic acids cannot explain the reported observations and is unlikely to represent an atmospherically relevant new-particle formation mechanism.

Atmospheric new-particle formation is a major source of aerosol particles that influence air quality, cloud properties, and climate. Understanding the molecular mechanisms governing the initial steps of particle formation is therefore essential for accurately representing aerosol formation and its climatic effects in atmospheric models. Zhang et al. (2026c) recently proposed that hydrogen-bond–driven self-assembly of neutral carboxylic acids is a spontaneous and ubiquitous atmospheric new-particle formation mechanism. If correct, this would represent a fundamental shift in the current understanding of atmospheric nucleation. In this comment, we show that the proposed nucleation mechanism is not adequately supported by the observations or theoretical analysis presented in Zhang et al. The reported particle-composition measurements lack sufficient validation to establish the proposed molecular composition of the smallest particles and do not directly constrain the molecular processes responsible for the earliest stages of particle formation. Furthermore, using the thermodynamic data reported by Zhang et al., we demonstrate that cluster evaporation overwhelmingly exceeds growth by molecular collisions, resulting in negligible particle-formation rates under the reported atmospheric conditions. These kinetic and thermodynamic analyses demonstrate that hydrogen-bond–driven clustering of neutral carboxylic acids cannot explain the reported observations and is unlikely to represent an atmospherically relevant new-particle formation mechanism.

Atmospheric new-particle formation is a major source of aerosol particles that influence air quality, cloud properties, and climate. Understanding the molecular mechanisms governing the initial steps of particle formation is therefore essential for accurately representing aerosol formation and its climatic effects in atmospheric models. Zhang et al. (2026c) recently proposed that hydrogen-bond–driven self-assembly of neutral carboxylic acids is a spontaneous and ubiquitous atmospheric new-particle formation mechanism. If correct, this would represent a fundamental shift in the current understanding of atmospheric nucleation. In this comment, we show that the proposed nucleation mechanism is not adequately supported by the observations or theoretical analysis presented in Zhang et al. The reported particle-composition measurements lack sufficient validation to establish the proposed molecular composition of the smallest particles and do not directly constrain the molecular processes responsible for the earliest stages of particle formation. Furthermore, using the thermodynamic data reported by Zhang et al., we demonstrate that cluster evaporation overwhelmingly exceeds growth by molecular collisions, resulting in negligible particle-formation rates under the reported atmospheric conditions. These kinetic and thermodynamic analyses demonstrate that hydrogen-bond–driven clustering of neutral carboxylic acids cannot explain the reported observations and is unlikely to represent an atmospherically relevant new-particle formation mechanism.

Atmospheric new-particle formation is a major source of aerosol particles that influence air quality, cloud properties, and climate. Understanding the molecular mechanisms governing the initial steps of particle formation is therefore essential for accurately representing aerosol formation and its climatic effects in atmospheric models. Zhang et al. (2026c) recently proposed that hydrogen-bond–driven self-assembly of neutral carboxylic acids is a spontaneous and ubiquitous atmospheric new-particle formation mechanism. If correct, this would represent a fundamental shift in the current understanding of atmospheric nucleation. In this comment, we show that the proposed nucleation mechanism is not adequately supported by the observations or theoretical analysis presented in Zhang et al. The reported particle-composition measurements lack sufficient validation to establish the proposed molecular composition of the smallest particles and do not directly constrain the molecular processes responsible for the earliest stages of particle formation. Furthermore, using the thermodynamic data reported by Zhang et al., we demonstrate that cluster evaporation overwhelmingly exceeds growth by molecular collisions, resulting in negligible particle-formation rates under the reported atmospheric conditions. These kinetic and thermodynamic analyses demonstrate that hydrogen-bond–driven clustering of neutral carboxylic acids cannot explain the reported observations and is unlikely to represent an atmospherically relevant new-particle formation mechanism.

Atmospheric new-particle formation is a major source of aerosol particles that influence air quality, cloud properties, and climate. Understanding the molecular mechanisms governing the initial steps of particle formation is therefore essential for accurately representing aerosol formation and its climatic effects in atmospheric models. Zhang et al. (2026c) recently proposed that hydrogen-bond–driven self-assembly of neutral carboxylic acids is a spontaneous and ubiquitous atmospheric new-particle formation mechanism. If correct, this would represent a fundamental shift in the current understanding of atmospheric nucleation. In this comment, we show that the proposed nucleation mechanism is not adequately supported by the observations or theoretical analysis presented in Zhang et al. The reported particle-composition measurements lack sufficient validation to establish the proposed molecular composition of the smallest particles and do not directly constrain the molecular processes responsible for the earliest stages of particle formation. Furthermore, using the thermodynamic data reported by Zhang et al., we demonstrate that cluster evaporation overwhelmingly exceeds growth by molecular collisions, resulting in negligible particle-formation rates under the reported atmospheric conditions. These kinetic and thermodynamic analyses demonstrate that hydrogen-bond–driven clustering of neutral carboxylic acids cannot explain the reported observations and is unlikely to represent an atmospherically relevant new-particle formation mechanism.

Atmospheric new-particle formation is a major source of aerosol particles that influence air quality, cloud properties, and climate. Understanding the molecular mechanisms governing the initial steps of particle formation is therefore essential for accurately representing aerosol formation and its climatic effects in atmospheric models. Zhang et al. (2026c) recently proposed that hydrogen-bond–driven self-assembly of neutral carboxylic acids is a spontaneous and ubiquitous atmospheric new-particle formation mechanism. If correct, this would represent a fundamental shift in the current understanding of atmospheric nucleation. In this comment, we show that the proposed nucleation mechanism is not adequately supported by the observations or theoretical analysis presented in Zhang et al. The reported particle-composition measurements lack sufficient validation to establish the proposed molecular composition of the smallest particles and do not directly constrain the molecular processes responsible for the earliest stages of particle formation. Furthermore, using the thermodynamic data reported by Zhang et al., we demonstrate that cluster evaporation overwhelmingly exceeds growth by molecular collisions, resulting in negligible particle-formation rates under the reported atmospheric conditions. These kinetic and thermodynamic analyses demonstrate that hydrogen-bond–driven clustering of neutral carboxylic acids cannot explain the reported observations and is unlikely to represent an atmospherically relevant new-particle formation mechanism.

Atmospheric new-particle formation is a major source of aerosol particles that influence air quality, cloud properties, and climate. Understanding the molecular mechanisms governing the initial steps of particle formation is therefore essential for accurately representing aerosol formation and its climatic effects in atmospheric models. Zhang et al. (2026c) recently proposed that hydrogen-bond–driven self-assembly of neutral carboxylic acids is a spontaneous and ubiquitous atmospheric new-particle formation mechanism. If correct, this would represent a fundamental shift in the current understanding of atmospheric nucleation. In this comment, we show that the proposed nucleation mechanism is not adequately supported by the observations or theoretical analysis presented in Zhang et al. The reported particle-composition measurements lack sufficient validation to establish the proposed molecular composition of the smallest particles and do not directly constrain the molecular processes responsible for the earliest stages of particle formation. Furthermore, using the thermodynamic data reported by Zhang et al., we demonstrate that cluster evaporation overwhelmingly exceeds growth by molecular collisions, resulting in negligible particle-formation rates under the reported atmospheric conditions. These kinetic and thermodynamic analyses demonstrate that hydrogen-bond–driven clustering of neutral carboxylic acids cannot explain the reported observations and is unlikely to represent an atmospherically relevant new-particle formation mechanism.

Atmospheric new-particle formation is a major source of aerosol particles that influence air quality, cloud properties, and climate. Understanding the molecular mechanisms governing the initial steps of particle formation is therefore essential for accurately representing aerosol formation and its climatic effects in atmospheric models. Zhang et al. (2026c) recently proposed that hydrogen-bond–driven self-assembly of neutral carboxylic acids is a spontaneous and ubiquitous atmospheric new-particle formation mechanism. If correct, this would represent a fundamental shift in the current understanding of atmospheric nucleation. In this comment, we show that the proposed nucleation mechanism is not adequately supported by the observations or theoretical analysis presented in Zhang et al. The reported particle-composition measurements lack sufficient validation to establish the proposed molecular composition of the smallest particles and do not directly constrain the molecular processes responsible for the earliest stages of particle formation. Furthermore, using the thermodynamic data reported by Zhang et al., we demonstrate that cluster evaporation overwhelmingly exceeds growth by molecular collisions, resulting in negligible particle-formation rates under the reported atmospheric conditions. These kinetic and thermodynamic analyses demonstrate that hydrogen-bond–driven clustering of neutral carboxylic acids cannot explain the reported observations and is unlikely to represent an atmospherically relevant new-particle formation mechanism.