Chlorine atoms (Cl) are highly reactive and can strongly influence the abundances of climate and air quality-relevant trace gases. Despite extensive research on molecular chlorine (Cl2), a Cl precursor, in the polar atmosphere, its sources in other regions are still poorly understood. Here we report the daytime Cl2 concentrations of up to 1 ppbv observed in a coastal area of Hong Kong, revealing a large daytime source of Cl2 (2.7 pptv s−1 at noon). Field and laboratory experiments indicate that photodissociation of particulate nitrate by sunlight under acidic conditions (pH < 3.0) can activate chloride and account for the observed daytime Cl2 production. The high Cl2 concentrations significantly increased atmospheric oxidation. Given the ubiquitous existence of chloride, nitrate, and acidic aerosols, we propose that nitrate photolysis is a significant daytime chlorine source globally. This so far unaccounted for source of chlorine can have substantial impacts on atmospheric chemistry.

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Unsaturated esters are emitted into the atmosphere from biogenic and anthropogenic sources. Their atmospheric degradation through reactions with the main atmospheric oxidants (OH, O3, NO3, Cl) contributes to the formation of important secondary pollutants. Kinetic and mechanistic parameters for these reactions are highly required in order to estimate the atmospheric lifetimes and hence the impacts of these important classes of VOCs. In this study, the gas-phase rate coefficients of the reaction of OH radical and O3 with a series of unsaturated esters are reported. The esters investigated include methyl methacrylate (MMA), ethyl methacrylate (EMA), n-propyl methacrylate (nPMA), n-butyl methacrylate (nBMA), iso-propyl methacrylate (iPMA), iso-butyl methacrylate (iBMA) and fully deuterated methyl methacrylate (MMA-D8). The measurement combined the pulsed laser photolysis-laser induced fluorescence for the OH studies in the temperature range 257-376K and a 7300 L atmospheric simulation chamber for the O3 reactions at 291 ± 2K. This work provides the first temperaturedependence studies of OH reaction with EMA, nPMA, iPMA and iBMA and of O3 reaction with nPMA, iPMA and iBMA at room temperature. The obtained data are discussed in terms of the structure reactivity relationships and their atmospheric consequences by estimating the atmospheric lifetimes for the studied esters with respect to O3, OH radical and other oxidant in the troposphere.

Water-soluble fluorescent conjugated polymers can be used as an optical platform in highly sensitive DNA sensors. Here we report a simple label-free DNA sensor using poly(3-alkoxy-4-methylthiophene) to recognize and detect different oligonucleotide targets related to the YMDD gene mutation of hepatitis B virus. The concentration of surfactant Triton X-100, NaCl, the oligonucleotide capture probe and the oligonucleotide hybridization conditions have a great impact on fluorescence intensity. Under the optimum conditions, two types of oligonucleotide targets involving YMDD gene mutation of hepatitis B virus were successfully recognized. Moreover, there was a linear relationship between fluorescence intensity and the concentration of oligonucleotide target. The detection limit of the wild-type hepatitis B virus target is 88 pmol L(-1).