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 laser ionization selectivity of APLI is one factor contributing to the selectivity, but under LC conditions, APPI suffers from another effect: The VUV light utilized by APPI does not penetrate deep into the ion source geometry, because the solvents used by LC, which are present as vapor in the ion source, strongly absorb the VUV light. For the UV light of APLI the LC solvents are virtually transparent, thus APLI allows the generation of ions in the entire ion source volume. In contrast to other ionization methods such as electrospray ionization (ESI) and atmospheric-pressure chemical ionization (APCI), APLI allows the generation of