UNCERTAINLY CALCULATION IN AEROSOL MEASUREMENTS

Abstract

Mass measurements of particles in the atmosphere are important for regulatory and scientific purposes. In nearly all of the countries, particulates ≤10 µm in aerodynamic size (PM10) is one of the most significant parameters of National Ambient Air Quality Standards (NAAQS). In India, as given in NAAQS, the PM10 regulatory limit is 60 µg m-3 which is based on the annual mean weight of samples (minimum 104) annually at a specific site taken for two/three days in a week for 24-hour. In this study, the components of uncertainty involved in the filter-based sampling of PM10 along with the gravimetric determination of mass have been calculated. As per the EPA guidelines, PM10 mass was monitored for a year at NPL (National Physical Laboratory), New Delhi from January 2014 to January 2015. Monitoring of PM10 was done using the gravimetric method. Polyaromatic hydrocarbons (PAHs) are the compound which consists of multiple benzene rings bonded in straight, groups or angular forms. They are also found in atmospheric aerosols. In the atmosphere, they can be emitted primarily as a result of incomplete combustion of natural sources (fossil fuels, forest fires, smoke etc.) or anthropogenic sources (coal burning, vehicular emissions, smoke, etc.) or secondarily by atmospheric processes. Depending on the anthropogenic sources, PAHs may occur in significant concentration in urban and industrial ambient air, i.e., bounded with particulate matter (PM). Benzo(a)pyrene (BaP) is among the most toxic and carcinogenic PAHs. Both PM10 and BaP are among the 12 criteria pollutants listed in Indian National Ambient Air Quality Standards (NAAQS). BaP concentration in PM10 collected in a representative site of New Delhi was studied during the year 2014–2015. The uncertainty components in measurements were also estimated along with statistical analysis. iv In this study, the concentration of metals/element of air quality importance in PM10 were also determined. There are three metal pollutants which are listed as the criteria pollutant in the National Ambient Air Quality Standards (NAAQS) i.e., Arsenic (As), Nickel (Ni) and Lead (Pb). PM10 was collected on quartz filter from January 2014 to January 2015 for the determination of metal concentration in it. 104 PM10 sample was digested in the microwave digestion system and the metals were analyzed on Inductively Coupled Plasma-Optical Emission Spectrometer instrument (ICP-OES) and the metal/element concentration of As, Ni and Pb were calculated. The regulated limits in NAAQS of these metals/elements are Pb -1 µg m -3 , Ni - 20 ng m -3 , As - 6 ng m-3 respectively. The studies were carried out to monitor the compliance of metal concentration with reference to the regulatory limits.