Identifying the spatiotemporal variations in ozone formation regimes across China from 2005 to 2019 based on polynomial simulation and causality analysis

Ozone formation regimes are closely related to the ratio of volatile organic compounds (VOCs) to NOx. Different ranges of HCHO/NO2 indicate three formation regimes, including VOC-limited, transitional, and NOx-limited regimes. Due to the unstable interactions between a diversity of precursors, the range of the transitional regime, which plays a key role in identifying ozone formation regimes, remains unclear. To overcome the uncertainties from single models and the lack of reference data, we employed two models, polynomial simulation and convergent cross-mapping (CCM), to identify the ranges of HCHO/NO2 across China based on ground observations and remote sensing datasets. The ranges of the transitional regime estimated by polynomial simulation and CCM were [1.0, 1.9] and [1.0, 1.8]. Since 2013, the ozone formation regime has changed to the transitional and NOx-limited regime all over China, indicating that ozone concentrations across China were mainly controlled by NOx. However, despite the NO2 concentrations, HCHO concentrations continuously exert a positive influence on ozone concentrations under transitional and NOx-limited regimes. Under the circumstance of national NOx reduction policies, the increase in VOCs became the major driver for the soaring ozone pollution across China. For an effective management of ozone pollution across China, the emission reduction in VOCs and NOx should be equally considered.

The Impact of Arid Climate on the Indoor Thermal Comfort in the South-East of Morocco

The main objective of this work is to study the heat transfer through an administrative building’s envelope in Errachidia City in Morocco. A numerical simulation based on the finite element method was made to describe the effect of introducing several thermal insulators (air, hemp wool, glass wool, rock wool, and extruded polystyrene) of different thicknesses (5 cm, 10 cm, and 15 cm) on the heat transfer through the building’s envelope under different climatic conditions. For the stationary regime, the summer period was chosen on August 7th, 2019, at 17 h, while the winter period was opted on January 1st, 2020, at 7 h. Otherwise, for the transitional regime, the summer period was chosen from August 1st to 8th, 2019, and the winter period from January first to 8th, 2020. The physical model analyzes the temperature variation at the different layers of the wall. It depends on the indoor temperature, the instantaneous climatic conditions of the outdoor air, solar radiations, and the thermal properties of the building’s envelope. The results show that the air gap is a good thermal insulator; it acts as a damper of temperature and heat flux.

Transition to Periodic Behaviour of Flow Past a Circular Cylinder under the Action of Fluidic Actuation in the Transitional Regime

This study focuses on the numerical investigation of the underlying mechanism of transition from chaotic to periodic dynamics of circular cylinder wake under the action of time-dependent fluidic actuation at the Reynolds number = 2000. The forcing is realized by blowing and suction from the slits located at ±90∘ on the top and bottom surfaces of the cylinder. The inverse period-doubling cascade is the underlying physical mechanism underpinning the wake transition from mild chaos to perfectly periodic dynamics in the spanwise-independent, time-dependent forcing at twice the natural vortex-shedding frequency.

Spatial and temporal changes of the ozone sensitivity in China based on satellite and ground-based observations

Ground-level ozone (O3) pollution has been steadily getting worse in most parts of eastern China during the past 5 years. The non-linearity of O3 formation with its precursors like nitrogen oxides (NOx= NO + NO2) and volatile organic compounds (VOCs) are complicating effective O3 abatement plans. The diagnosis from space-based observations, i.e. the ratio of formaldehyde (HCHO) columns to tropospheric NO2 columns (HCHO / NO2), has previously been proved to be highly consistent with our current understanding of surface O3 chemistry. HCHO / NO2 ratio thresholds distinguishing O3 formation sensitivity depend on regions and O3 chemistry interactions with aerosol. To shed more light on the current O3 formation sensitivity over China, we have derived HCHO / NO2 ratio thresholds by directly connecting satellite-based HCHO / NO2 observations and ground-based O3 measurements over the major Chinese cities in this study. We find that a VOC-limited regime occurs for HCHO / NO2 < 2.3, and a NOx-limited regime occurs for HCHO / NO2 > 4.2. The HCHO / NO2 between 2.3 and 4.2 reflects the transition between the two regimes. Our method shows that the O3 formation sensitivity tends to be VOC-limited over urban areas and NOx-limited over rural and remote areas in China. We find that there is a shift in some cities from the VOC-limited regime to the transitional regime that is associated with a rapid drop in anthropogenic NOx emissions, owing to the widely applied rigorous emission control strategies between 2016 and 2019. This detected spatial expansion of the transitional regime is supported by rising surface O3 concentrations. The enhanced O3 concentrations in urban areas during the COVID-19 lockdown in China indicate that a protocol with simultaneous anthropogenic NOx emissions and VOC emissions controls is essential for O3 abatement plans.

Identifying the spatiotemporal variations of ozone formation regimes across China from 2005 to 2019 based on polynomial simulation and causality analysis

Ozone formation regimes are closely related to the ratio of VOCs to NOx. Different ranges of HCHO/NO2 indicate three formation regimes, including VOCs-limited, transitional and NOx-limited regimes. Due to the unstable interactions between a diversity of precursors, the range of transitional regime, which plays a key role in identifying ozone formation regimes, remains unclear. To overcome the uncertainties from single models and the lack of reference data, we employed two models, polynomial simulation and Convergent Cross Mapping (CCM), to identify the ranges of HCHO/NO2 across China based on ground observations and remote sensing datasets. The ranges of transitional regime estimated by polynomial simulation and CCM were [1.0, 1.9] and [1.0, 1.8]. Since 2013, ozone formation regime has changed to the transitional and NOx-limited regime all over China, indicating ozone concentrations across China were mainly controlled by NOx. However, despite the NO2 concentrations, HCHO concentrations continuously exert a positive influence on ozone concentrations under transitional and NOx-limited regimes. Under the circumstance of national NOx-reduction policies, the increase of VOCs became the major driver for the soaring ozone pollution across China. For an effective management of ozone pollution across China, the emission-reduction of VOCs and NOx should be equally considered.