Barometer Simultaneous barometric readings from across a network of weather stations allow maps of air pressure to be produced, which were the first form of the modern weather map when created in the 19th century. Isobars, lines of equal pressure, when drawn on such a map, give a contour map showing areas of high and low pressure. Localized high atmospheric pressure acts as a barrier to approaching weather systems, diverting their course. Atmospheric lift caused by low-level wind convergence into the surface brings clouds and sometimes precipitation. The larger the change in pressure, especially if more than 3.5 hPa (0.1 inHg),
Atmospheric-pressure chemical ionization ionized, which produce N. The evaporated mobile phase of LC acts as the ionization gas and reactant ions. If water is the only solvent in the evaporated mobile phase, the excited nitrogen molecular ions N would react with HO molecules to produce water cluster ions H(HO). Then, analyte molecules M are protonated by the water cluster ions. Finally, the ionization products MH(HO) transfer out from the atmospheric-pressure ion source. Declustering (removal of water molecules from the protonated analyte molecule) of MH(HO) takes place at the high vacuum of the mass analyzer. The analyte molecule ions detected by MS are [M+H].