Atmospheric Monitoring of PM₂.₅, PM₁₀₋₂.₅, PM₁₀, Arsenic and Carbonaceous Aerosol at Wainuiomata
Authors:   , Singh Chandar 
Published: November 2021

<p>Air pollution is harming our health and that of our children and parents. Air pollution causes many harmful effects, ranging from premature death, to headaches, coughing and asthma attacks. Previous studies (2008-2009) of particulate matter at Wainuiomata, Lower Hutt showed that biomass burning was primarily responsible for peak PM₂.₅ and PM₁₀ concentrations and exceedances of the National Environmental Standard (NES) and the New Zealand Ambient Air Quality Guidelines (NZAAQG). Arsenic was also found to be associated with biomass burning sources during winter at Wainuiomata. The source of arsenic was considered to be due to the use of copper chromium arsenate (CCA) treated timber as solid fuel for fires for domestic heating. While particulate matter pollution from domestic fires itself presents a health risk for the exposed population, the addition of arsenic to the mix enhances the potential risk. The use of CCA treated timber was unlikely to be used on a regular basis hence the peak arsenic concentrations did not always coincide with peak contributions from domestic fires and that the use of CCA – treated timber is more intermittent and opportunistic.  This work compared several different analytical methodologies for the determination of arsenic in air particulate matter. The primary purpose was to use a standard analytical method as recommended by the NZAAQ guidelines and compare those results with the Ion Beam Analysis (IBA) and X-ray Fluorescence Spectroscopy (XRF) methods used to determine arsenic concentrations in previous studies.  Through this collaborative research with GNS Science and GWRC, it was found that annual PM₁₀ and PM₂.₅ averages were well within the NZAAQG values of; 20 μg m⁻³ and 10 μg m⁻³ respectively. There was a much correlated seasonal and temporal variations observed for black carbon (BC), PM₂.₅ and arsenic concentrations. The overall concentrations of BC, PM₂.₅ and PM₁₀ have decreased significantly in the Wainuiomata airshed compared to previous studies as reported in 2009 with fewer exceedances of the NES and NZAAQG on a 24 hour daily average.  The overall weighted mean arsenic concentration as measured by GF-AAS was 6.3 ± 0.8 ng m⁻³ and that measured by XRF and IBA was 3.8 ± 2.0 ng m⁻³ and 3.1 ± 5.9 ng m⁻³ respectively. The XRF and IBA arsenic concentrations were consistently lower than that of GF-AAS. The two annual arsenic averages (GF-AAS) were 6.5 ± 0.9 ng m⁻³ and 5.9 ± 0.7 ng m⁻³ respectively, for the entire sampling period. In both the cases the NZAAQG value of 5.5 ng m⁻³ were exceeded. The exceedance in the second year of sampling was not statistically significant as the guideline value 5.5 ngm⁻³ falls within the given uncertainty of the measured annual averages for arsenic.  However, it is definitely an area of concern as the overall arsenic concentrations during winter periods was 12.2 ± 1.0 ng m⁻³. Moreover, burning CCA treated timber is effectively banned through regional plan rules and the problem presents itself as one of enforcement and/or public education.  The inter-method comparison showed that IBA technique can be used for “screening” purposes due to high limit of detection (LOD) and analytical noise. While XRF can still be used interchangeably with GF-AAS but with Teflon or thinner filter membrane, for long term environmental monitoring of arsenic and other elemental compositions. Given the excellent recoveries of 99.2 ± 0.8% for duplicate spiked analysis and 102.7 ± 0.9% for lab blank filters spiked analysis, at 95% confidence intervals, GF-AAS method is highly reproducible and should be used in the determination of arsenic in ambient air for the purpose of comparing with the NZAAQG values.</p>