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A new compound with implications in scale and corrosion control has been isolated and its solubility measured under varying conditions of temperature and ionic strength from 25 to 75 °C and from 1 to 3 M ionic strength. Ferrous phosphonate was formed using the phosphonate nitrilotris(methylene phosphonic acid) (NTMP) and was found to have the stoichiometry Fe2.5HNTMP. Using a complexation and speciation model, the stability constants for the complexation of iron(II) with phosphonate were calculated, and the solubility product constant was derived for each temperature and ionic strength; at 25 °C and 1 M ionic strength, K sp = 10-31.2. The temperature (T, K) and ionic strength (I, M) dependence of the negative logarithm of the ferrous phosphonate solubility product constant (pK sp) was determined to be:  pK sp = 39.54 − 6.14I 1/2 + 2.18I − 1315/T. In simulated calculations using actual field data to compare iron and calcium phosphonates independently, ferrous salts were predicted to form in all instances and matured calcium salts were predicted to form occasionally. Furthermore, a relationship was established whereby the concentration of free iron in a calcium−iron−phosphonate system can be predicted for a given system.

A laser spectrometer based on difference-frequency generation in periodically poled LiNbO3 (PPLN) has been used to quantify atmospheric formaldehyde with a detection limit of 0.32 parts per billion in a given volume (ppbV) using specifically developed data-processing techniques. With state-of-the-art fiber-coupled diode-laser pump sources at 1083 nm and 1561 nm, difference-frequency radiation has been generated in the 3.53-micrometers (2832-cm-1) spectral region. Formaldehyde in ambient air in the 1- to 10-ppb V range has been detected continuously for nine and five days at two separate field sites in the Greater Houston area operated by the Texas Natural Resource Conservation Commission (TNRCC) and the Houston Regional Monitoring Corporation (HRM). The acquired spectroscopic data are compared with results obtained by a well-established wet-chemical o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA) technique.

Abstract.A one-week in situ intercomparison campaign was completed on the Rice University campus for measuring HCHO using three different techniques, including a novel op-