A Wintertime Impact of Dilution on Transformation Rate in the Planetary Boundary Layer

Abstract

ABSTRACT. The effects of dilution on photochemical reactions of trace gases released from spontaneous combustion processes near open cast coalmines in winter have been examined with a view to assessing the impact of meteorology on atmospheric chemical reactions. Daytime observed gas concentrations vary significantly due to dilution and transformation at average relative humidity of 48.9 ± 4.3 % and temperature of 14.4 ± 0.6 o C. Dilution occurred during the day with rise in wind speed. This yielded dilution rate constants of 1.0 × 10 -3 min -1 for CO, 2.5 × 10 -3 min -1 for NO, 1.9 × 10 -3 min -1 for NO 2 , 8.4 × 10 -4 min -1 for H 2 S, 9.8 × 10 -4 min -1 for SO 2 and 1.6 × 10 -3 min -1 for O 3 . H 2 S and SO 2 were observed to exhibit very close resemblance in diurnal variations. The average daytime and night time concentrations of the observed H 2 S were 31.5 ± 13.4 ppb and 171.7 ± 15.9 ppb and 31.6 ± 13.2 ppb and 128.5 ± 18.1 ppb for SO 2 . Chemical reaction rates were evaluated over a temperature range between 0 and 20 o C and mean surface pressure of 850.4 ± 2.7 mbar for the trace inorganic gases. Over this temperature range and surface pressure, transformation rates of SO 2 and H 2 S are 0.023 %·h

A case study in the wintertime Vaal Triangle Air-Shed Priority Area on the utility of the nitrogen stable isotopic composition of aerosol nitrate to identify NOx sources

“…The fate of NO x produced in the Highveld and Vaal regions includes dry and wet deposition and conversion to aerosol nitrate. The local recirculation time scale is 2 to 9 days (Freiman and Piketh 2003;Collett et al 2010;Igbafe et al 2015), allowing for complete NO x conversion to nitrate, such that aerosol nitrate concentrations in the Highveld/Vaal area are primarily influenced by local NO x emissions. Similarly, local industrial emissions of SO 2 make a considerable contribution to sulfate aerosols, the main component of the summer and winter haze layer in this region (Piketh et al 1999).…”

Indoor Smoke Emissions from Direct-Fires in Urban Households in Benin City Area of Midwestern Nigeria

“…With a considerable number of houses in Benin City utilising kerosene stoves as a primary indoor source of heat energy generation; and occasionally kerosene lanterns and candles for lighting during power failure and mosquito coils which are cheaper than spray insecticides, it is most likely that many households in the region are inevitably highly polluted. In the past, several studies on the impact of CO on humans over Benin City and environs in Nigeria have been undertaken [6][7][8], but none of the studies has established the vertical and temporal distribution of indoor pollution. Studies have shown that the impact of the huge emissions from indoor fires have significant health problem to residents [9][10][11][12].…”