The size and chemical composition of the particles evolve with time through coagulation, condensation, and chemical reactions. Occasionally volcanic eruptions result in huge amounts of primary and secondary aerosols both at the ground and in the stratosphere (Boulon et al. The main precursor gases are emitted from fossil fuel combustion, but fires and biogenic emissions of volatile organic compounds (VOCs) are also important. Secondary aerosols consist of mixtures of compounds the main components are sulphate, nitrate, and OC. Secondary aerosols are small they range in size from a few nanometres up to 1 µm and have lifetimes of days to weeks. A considerable fraction of the mass of secondary aerosols is formed through cloud processing (Ervens et al. Secondary aerosol particles are produced in the atmosphere from precursor gases by condensation of vapours on pre-existing particles or by nucleation of new particles. Primary BC and OC containing aerosols are generally smaller than 1 µm. Its main sources are the combustion of fossil fuels (such as gasoline, oil, and coal), wood, and other biomass. BC is the main anthropogenic light-absorbing constituent present in aerosols. Combustion processes, biomass burning, and plant/microbial materials are sources of carbonaceous aerosols, including both organic carbon (OC) and solid black carbon (BC). These coarse aerosols have short atmospheric lifetimes, typically only a few days. Inorganic primary aerosols are relatively large (often larger than 1 μm) and originate from sea spray, mineral dust, and volcanoes. Primary aerosols consist of both inorganic and organic components. Aerosol particles are either emitted directly to the atmosphere (primary aerosols) or produced in the atmosphere from precursor gases (secondary aerosols). Their variability is due to the numerous sources and varying formation mechanisms (Figure 1). As shown by examples from field experiments, the instrument provides sufficient precision (3-9%), even at low ambient concentrations, to resolve vertical gradients and calculate surface-atmosphere exchange fluxes undertypical meteorological conditions of the atmospheric surface layer using the aerodynamic gradient technique.Atmospheric aerosols are suspensions of liquid, solid, or mixed particles with highly variable chemical composition and size distribution (Putaud et al. The instrument demonstrates very good linearity and accuracy for liquid and selected gas phase calibrations over typical ambient concentration ranges. Through the use of syringe pumps, IC preconcentration columns, and high-quality purified water, the system achieves detection limits (3sigma-definition) under field conditions of typically: 136/207,135/114, 29/ 22,119/92, and 189/159 ng m(-3) for NH3/NH4+, HNO3/NO3-, HONO/ NO2-, HCl/Cl- and SO2/SO4(2-), respectively. Online (real-time) analysis using ion chromatography (IC) for anions and flow injection analysis (FIA) for NH4+ and NH3 provide a half-hourly averaged gas and aerosol gradients within each hour. Gas and aerosol samples are collected simultaneously at two heights using rotating wet-annular denuders and steam-jet aerosol collectors, respectively. Here, we present a new automated instrument for semicontinuous gradient measurements of water-soluble reactive trace gas species (NH3, HNO3, HONO, HCl, and SO2) and their related aerosol compounds (NH4+, NO3-, Cl-, SO4(2-)).
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