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),
Desorption atmospheric pressure photoionization by the vacuum ultraviolet light and consequently sampled into a mass spectrometer. DAPPI can detect a range of both polar and non-polar compounds, but is most sensitive when analyzing neutral or non-polar compounds. This technique also offers a selective and soft ionization for highly conjugated compounds. The history of desorption atmospheric pressure photoionization is relatively new, but can be traced back through developments of ambient ionization techniques dating back to the 1970s. DAPPI is a combination of popular techniques, such as, atmospheric pressure photoionziation (APPI) and surface desorption techniques. The photoionization techniques were first developed in the late 1970s and