The accurate measurement of pH in atmospheric wet deposition is an essential and critically important component in the monitoring of atmospheric wet deposition for trends in the acidity and overall air quality. Atmospheric wet deposition is, in general, a low ionic strength, unbuffered solution. Special precautions, as detailed in this test method, are necessary to ensure accurate pH measurements (1). Special emphasis must be placed on minimizing the effect of the residual liquid junction potential bias.

This test method is applicable only to the measurement of pH in atmospheric wet deposition. Its use in other applications may result in inaccuracies.

Fig. 1 provides a frequency distribution of precipitation pH values measured in conjunction with a national monitoring program within the United States. These data are an indication of the range of pH values common to atmospheric wet deposition.

FIG. 1 Frequency Distribution of Measured Laboratory pH of Atmospheric Wet Deposition From the 1984 National Atmospheric Deposition Program (NADP)/National Trends Network (NTN)

1. Scope

1.1 This test method is applicable to the determination of pH in atmospheric wet deposition samples by electrometric measurement using either a pH half cell with a reference probe or a combination electrode as the sensor.

1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

ASTM Standards

D1129 Terminology Relating to Water

D1193 Specification for Reagent Water

D1356 Terminology Relating to Sampling and Analysis of Atmospheres

D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water

D5012 Guide for Preparation of Materials Used for the Collection and Preservation of Atmospheric Wet Deposition

D5111 Guide for Choosing Locations and Sampling Methods to Monitor Atmospheric Deposition at Non-Urban Locations

E1 Specification for ASTM Liquid-in-Glass Thermometers

Keywords

atmospheric deposition; hydrogen ion; low ionic strength solutions; pH; precipitation; wet deposition; Acidity, alkalinity, pH--chemicals; Acid rain; Atmospheric wet deposition (AWD); Calibration--air/atmospheric analysis instruments; Electrodes; Electrometric determination; Glass electrodes; Hydrogen ion exchange; Low ionic strength solutions; Nernstian response; pH; Residual junction/streaming potential; Workplace air/atmospheres;

ICS Code

ICS Number Code 71.040.50 (Physicochemical methods of analysis)

Citing ASTM Standards

[Back to Top]