Characteristics and source apportionment of some halocarbons in Hangzhou, eastern China during 2021

In recent years, eastern China has been identified as an important contributor to national and global emissions of halocarbons, some of which are ozone depletion substances (ODSs) that delay the recovery of the stratospheric ozone layer. However, the most recent characteristics and sources of halocarbons in eastern China remain unclear. Thus, hourly atmospheric observations of halocarbons were conducted in Hangzhou throughout 2021. The results showed that methylene chloride (CH₂Cl₂) was the most abundant halocarbon (2207 (25 %-75 % quantile: 1116-2848) ppt; parts per trillion) followed by chloromethane (CH₃Cl) (912 (683-1043) ppt), and 1,2-dichloroethane (CH₂ClCH₂Cl) (596 (292-763) ppt). Then, backward trajectory and potential source contribution function (PSCF) analysis show that the emission hot spots of halocarbons were concentrated in adjacent cities in Zhejiang and neighboring provinces in eastern China. Moreover, based on positive matrix factorization (PMF) analysis, industrial emission (38.7 %), solvent usage (32.6 %), and the refrigeration sector and biomass burning (23.7 %) were the main sources of halocarbons (observed in this study). This study reveals high concentrations and potential sources of halocarbons in eastern China, which are important for studying the recovery of the ozone layer.

Air quality in Mecca and surrounding holy places in Saudi Arabia during Hajj: initial survey

The Arabian Peninsula experiences severe air pollution, the extent and sources of which are poorly documented. Each year in Saudi Arabia this situation is intensified during Hajj, the Holy Pilgrimage of Islam that draws millions of pilgrims to Mecca. An initial study of air quality in Mecca and surrounding holy sites during the 2012 Hajj (October 24-27) revealed strongly elevated levels of the combustion tracer carbon monoxide (CO, up to 57 ppmv) and volatile organic compounds (VOCs) along the pilgrimage route-especially in the tunnels of Mecca-that are a concern for human health. The most abundant VOC was the gasoline evaporation tracer i-pentane, which exceeded 1200 ppbv in the tunnels. Even though VOC concentrations were generally lower during a follow-up non-Hajj sampling period (April 2013), many were still comparable to other large cities suffering from poor air quality. Major VOC sources during the 2012 Hajj study included vehicular exhaust, gasoline evaporation, liquefied petroleum gas, and air conditioners. Of the measured compounds, reactive alkenes and CO showed the strongest potential to form ground-level ozone. Because the number of pilgrims is expected to increase in the future, we present emission reduction strategies to target both combustive and evaporative fossil fuel sources.

Temperature Dependence of the HO2 + ClO Reaction. 2. Reaction Kinetics Using the Discharge-Flow Resonance-Fluorescence Technique

The total rate coefficient, k3, for the reaction HO2 + ClO --> products has been determined over the temperature range of 220-336 K at a total pressure of approximately 1.5 Torr of helium using the discharge-flow resonance-fluorescence technique. Pseudo-first-order conditions were used with both ClO and HO2 as excess reagents using four different combinations of precursor molecules. HO2 molecules were formed by using either the termolecular association of H atoms in an excess of O2 or via the reaction of F atoms with an excess of H(2)O(2). ClO molecules were formed by using the reaction of Cl atoms with an excess of O3 or via the reaction of Cl atoms with Cl(2)O. Neither HO2 nor ClO were directly observed during the course of the experiments, but these species were converted to OH or Cl radicals, respectively, via reaction with NO prior to their observation. OH fluorescence was observed at 308 nm, whereas Cl fluorescence was observed at approximately 138 nm. Numerical simulations show that under the experimental conditions used secondary reactions did not interfere with the measurements; however, some HO2 was lost on conversion to OH for experiments in excess HO2. These results were corrected to compensate for the simulated loss. At 296 K, the rate coefficient was determined to be (6.4 +/- 1.6) x 10(-12) cm3 molecule(-1) s(-1). The temperature dependence expressed in Arrhenius form is (1.75 +/- 0.52) x 10-12 exp[(368 +/- 78)/T] cm3 molecule(-1) s(-1). The Arrhenius expression is derived from a fit weighted by the reciprocal of the measurement errors of the individual data points. The uncertainties are cited at the level of two standard deviations and contain contributions from statistical errors from the data analysis in addition to estimates of the systematic experimental errors and possible errors from the applied model correction.