Photooxidation Reactions of Ethyl 2-Methylpropionate (E2MP) and Ethyl 2,2-Dimethylpropionate (E22DMP) Initiated by OH Radicals: An Experimental and Computational Study

The relative rate (RR) technique was used for the measurement of OH-initiated photooxidation reactions of ethyl 2-methylpropionate (E2MP) and ethyl 2,2-dimethylpropionate (E22DMP) in the temperature range of 268-363 K at 760 Torr. In addition to this, the thermodynamic and kinetic parameters for the title reactions were theoretically investigated using CCSD(T)/cc-pVTZ//M06-2X/6-311++G(2d,2p) level of theory in the temperature range of 200-400 K using canonical variational transition state theory (CVT) in combination with small curvature tunneling (SCT) method. The rate coefficients at (298 ± 2) K were measured to be k_E2MP+OH = (2.71 ± 0.79) × 10^-12 cm³ molecule^-1 s^-1 and k_E22DMP+OH = (2.58 ± 0.80) × 10^-12 cm³ molecule^-1 s^-1. The degradation mechanisms for the title reactions were investigated in the presence of O₂ using gas chromatography with mass spectrometry (GC-MS) and gas chromatography with infrared spectroscopy (GC-IR). From the recognized products, the possible product degradation mechanisms were predicted. In addition to this, the atmospheric lifetimes (ALs), lifetime-corrected radiative forcing (RF), global warming potential (GWPs) and photochemical ozone creation potentials (POCPs) were calculated to further understand the environmental impact of these molecules on the Earth's troposphere.

Strong impact of wildfires on the abundance and aging of black carbon in the lowermost stratosphere

Unique information about the abundance and evolution of wildfire-emitted black carbon (BC) in the lowermost part of the stratosphere (LMS) was obtained from long-term airborne measurements made in cooperation with Lufthansa through the Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) project, part of the In-service Aircraft for a Global Observing System (IAGOS) framework. Our results demonstrate that wildfires can dramatically increase BC mass concentration in the LMS, substantially enhance regional climate forcing, and are a challenge for model simulations. Climate change is expected to increase the frequency and spread of wildfires. Thus, recording a present-day baseline with extensive and long-term measurements should help to constrain model estimations of the climate impact of BC and foster our fundamental understanding of future climate change.

Wildfires inject large amounts of black carbon (BC) particles into the atmosphere, which can reach the lowermost stratosphere (LMS) and cause strong radiative forcing. During a 14-month period of observations on board a passenger aircraft flying between Europe and North America, we found frequent and widespread biomass burning (BB) plumes, influencing 16 of 160 flight hours in the LMS. The average BC mass concentrations in these plumes (∼140 ng·m⁻³, standard temperature and pressure) were over 20 times higher than the background concentration (∼6 ng·m⁻³) with more than 100-fold enhanced peak values (up to ∼720 ng·m⁻³). In the LMS, nearly all BC particles were covered with a thick coating. The average mass equivalent diameter of the BC particle cores was ∼120 nm with a mean coating thickness of ∼150 nm in the BB plume and ∼90 nm with a coating of ∼125 nm in the background. In a BB plume that was encountered twice, we also found a high diameter growth rate of ∼1 nm·h⁻¹ due to the BC particle coatings. The observed high concentrations and thick coatings of BC particles demonstrate that wildfires can induce strong local heating in the LMS and may have a significant influence on the regional radiative forcing of climate.

Source identification of reactive hydrocarbons and oxygenated VOCs in the summertime in Beijing

It is important to identify the sources of reactive volatile organic compounds (VOCs) in Beijing for effective ground-level ozone abatement. In this paper, semihourly measurements of hydrocarbons and oxygenated VOCs (OVOCs) were taken at an urban site in Beijing in August2005. C2-C5 alkenes, isoprene, and C1-C3 aldehydes were determined as "key reactive species" by their OH loss rates. Principal component analysis (PCA) was used to define the major sources of reactive species and to classify the dominant air mass types at the sampling site. Vehicle exhaust was the largest contributor to reactive alkenes. More aged air masses with enriched OVOCs traveled mainly from the east or southeast of Beijing. The OVOC sources were estimated by a least-squares fit approach and included primary emissions, secondary sources, and background. Approximately half of the C1-C3 aldehydes were attributed to secondary sources, while regional background accounted for 21-23% of the mixing ratios of aldehydes. Primary anthropogenic emissions were comparable to biogenic contributions (10-16%).