Evaluation of the daytime tropospheric loss of 2-methylbutanal

Saturated aldehydes, e.g. 2-methylbutanal (2MB, CH3CH2CH(CH3)C(O)H), are emitted into the atmosphere by several biogenic sources. The first step in the daytime atmospheric degradation of 2MB involves gas-phase reactions initiated by hydroxyl (OH) radicals, chlorine (Cl) atoms and/or sunlight. In this work, we report the rate coefficients for the gas-phase reaction of 2MB with OH (kOH) and Cl (kCl) together with the photolysis rate coefficient (J) in the ultraviolet solar actinic region in Valencia (Spain) at different times of the day. The temperature dependence of kOH was described in the 263–353 K range by the following Arrhenius expression: kOH(T)=(8.88±0.41)×10-12 exp[(331±14)/T] cm3 molecule-1 s-1. At 298 K, the reported kOH and kCl are (2.68±0.07)×10-11 cm3 molecule-1 s-1 and (2.16±0.16)×10-11 cm3 molecule-1 s-1. Identification and quantification of the gaseous products of the Cl-reaction and those from the photodissociation of 2MB were carried out in a smog chamber by different techniques (Fourier transform infrared spectroscopy, proton transfer time-of-flight mass spectrometry, and gas chromatography coupled to mass spectrometry). The formation and size distribution of secondary organic aerosols formed in the Cl-reaction was monitored by a fast mobility particle sizer spectrometer. A discussion on the relative importance of the first step in the daytime atmospheric degradation of 2MB is presented together with the impact of the degradation products in marine atmospheres.

Protecting the Atmosphere as a ‘Global Common Good’

Atmospheric degradation has progressively been recognized as an international concern and several conventions have been adopted to regulate harmful activities. Nevertheless, international law on the protection of the atmosphere is still fragmented, and insufficient to respond to the multiple threats that it faces. This chapter aims to consider what are the possibilities and constraints in international law for recognizing the atmosphere as a global common good. The author examines: (i) what would be the legal consequences of recognizing the atmosphere as a global common good or as a common concern of humankind; (ii) whether the applicable international law already includes any references to the recognition of the atmosphere as such; and (iii) what are the challenges and constraints for doing so.

A zero-dimensional view of atmospheric degradation of levoglucosan (LEVCHEM_v1) using numerical chamber simulations

Here, we developed a zero-dimensional (0-D) modeling framework (LEVCHEM_v1) to provide insights into the atmospheric degradation of a key tracer emitted during biomass burning – levoglucosan (LEV), while additionally exploring its effects on the dynamics of secondary organic aerosols (SOA) and other gases. For this, we updated existing chemical mechanisms (homogeneous gas-phase chemistry and heterogeneous chemistry) in the BOXMOXv1.7 model to include the chemical degradation of LEV and its intermediary degradation products in both phases (gas and aerosol). In addition, we added a gas-particle partitioning mechanism to the model to account for the effect of evaporation and condensation on the phase-specific concentrations of LEV and its degradation products. Comparison of simulation results with measurements from various chamber experiments (spanning summer and winter conditions) show that the degradation timescale of LEV varied by phase, with gas-phase degradation occurring over ∼1.5–5 d and aerosol-phase degradation occurring over ∼8–36 h. These relatively short timescales suggest that most of the initial LEV concentration can be lost chemically or deposited locally before being transported regionally. We varied the heterogeneous reaction rate constant in a sensitivity analysis (for summer conditions only) and found that longer degradation timescales of LEV are possible, particularly in the aerosol phase (7 d), implying that some LEV may be transported regionally. The multiphase chemical degradation of LEV has effects on SOA and other gases. Several first- or second-generation products resulted from its degradation; most of the products include one or two carbonyl groups, one product contains a nitrate group, and a few products show the cleavage of C−C bonds. The relative importance of the products varies depending on the phase and the timing of the maximum concentration achieved during the simulation. Our estimated secondary organic aerosol SOA yields (4 %–32 %) reveal that conversion of LEV to secondary products is significant and occurs rapidly in the studied scenarios. LEV degradation affected other gases by increasing the concentrations of radicals and decreasing those of reactive nitrogen species. Decreases of the mixing ratios of nitrogen oxides appear to drive a more rapid increase in ozone compared with changes in volatile organic compounds levels. An important next step to confirm longer degradation timescales will be to extend the evaluation of the modeled LEV degradation beyond 3–6 h by using more extensive data from chambers and, possibly, from fire plumes. The mechanism developed here can be used in chemical transport models applied to fire plumes to trace LEV and its degradation products from source to deposition, to assess their atmospheric implications and to answer questions relevant to fire tracing, carbon and nitrogen cycling, and climate.