Real-Time Quantitative Assessment of Transport Induced Greenhouse Gases Emissions Profile in Lagos, Nigeria.

Over the years, scientists have established that when fossil fuels are burnt, the resultant effect is pollution of the ambient air with pollutants such as carbon monoxide (CO), methane (CH4), oxides of nitrogen (NOX), oxides of sulfur (SOX), volatile organic hydrocarbons and particulate matter and atmospheric greenhouse gases such as carbon dioxide (CO2) and methane (CH4) and heat-warming or cooling aerosols such as black soot and sulfate aerosols, respectively. These pollutants become present in the atmosphere at a concentration that can affect human health, the environment, and even society as a whole. Since around 1750, human activities have increased the concentration of CO2 and other greenhouse gases in the atmosphere by many tens of percent over the last two centuries. The Federal Government of Nigeria, through the office of National Environmental Standards and Regulation Enforcement Agency (NESREA), established guidelines and standards (limits) for the abatement and control of all forms of pollution through the establishment of Nigerian Ambient Air Quality Standards (NAAQS). Different studies on the impacts of urban road transportation on ambient air quality carried out by scholars have suggested that most pollutant gases in the atmosphere are traffic-related as a result of the combustion of petroleum-based products like gasoline and diesel in internal combustion engines. This study deployed a quantitative technique to determine the emissions profile of transport nodes in Ikeja, Lagos through the use of AEROQUAL 500s portable air monitoring equipment. Results showed that CO, CO2 and CH4 emissions were highest during the AM peak and PM peak periods and lower during the inter-peak period, while NOx emissions were relatively stable throughout the time periods.

Use of a Heated Graphite Scrubber as a Means of Reducing Interferences in UV-Absorbance Measurements of Atmospheric Ozone

A new solid-phase scrubber for use in conventional ozone photometers was investigated as a means of reducing interferences from other UV-absorbing species and water vapor. It was found that when heated to 100–130 °C, a tubular graphite scrubber efficiently removed up to 500 ppb ozone and ozone monitors using the heated graphite scrubber were found to be less susceptible to interferences from water vapor, mercury vapor, and aromatic volatile organic hydrocarbons (VOCs) compared to conventional metal oxide scrubbers. Ambient measurements from a graphite scrubber-equipped photometer and a co-located Federal Equivalent Method (FEM) ozone analyzer showed excellent agreement over 38 days of measurements and indicated no loss in the scrubber’s ability to remove ozone when operated at 130 °C. The use of a heated graphite scrubber was found to reduce the interference from mercury vapor to ≤ 3 % of that obtained using a packed-bed Hopcalite scrubber. For a series of substituted aromatic compounds (ranging in volatility and absorption cross section at 253.7 nm), the graphite scrubber was observed to consistently exhibit reduced levels of interference, typically by factors of 2.5 to 20 less than with Hopcalite. Conventional solid-phase scrubbers also exhibited complex VOC adsorption and desorption characteristics that were dependent upon the relative humidity (RH), volatility of the VOC, and the available surface area of the scrubber. This complex behavior involving humidity is avoided by use of a heated graphite scrubber. These results suggest that heated graphite scrubbers could be substituted in most ozone photometers as a means of reducing interferences from other UV-absorbing species found in the atmosphere. This could be particularly important in ozone monitoring for compliance with the U.S. Clean Air Act or for use in monitoring indoor air quality.

Dialkylsulfate formation in sulfuric acid-seeded secondary organic aerosol produced using an outdoor chamber under natural sunlight

Environmental context Laboratory and field studies have both provided evidence for organosulfate formation by esterification of H2SO4 with organic compounds in aerosols. Using an outdoor chamber, the production of dialkylsufate was measured for organic aerosols produced by photooxidation of various hydrocarbons in the presence of H2SO4 aerosol and NOx. The formation of organosulfates influences the decrease of both aerosol acidity and aerosol hygroscopicity. Abstract Secondary organic aerosols (SOA) were produced by the photooxidation of the volatile organic hydrocarbons (VOCs) isoprene, α-pinene and toluene, in the presence of excess amounts of sulfuric acid seed aerosol with varying NOx concentrations using a large, outdoor smog chamber. Aerosol acidity ([H+], μmol m–3) was measured using colorimetry integrated with a reflectance UV-visible spectrometer (C-RUV). The C-RUV technique measures aerosol acidity changes through the neutralisation of sulfuric acid with ammonia and the formation of dialkylsulfate, a diester of sulfuric acid. The concentration (μmol m–3) of dialkylsulfate in aerosol was estimated using the difference in [H+] obtained from C-RUV and particle-into-liquid-sampler ion chromatography (PILS-IC). The yield of dialkylsulfate (YdiOS) was defined as the dialkylsulfate concentration normalised by the concentrations of both the ammonium-free sulfate ([SO42–]free=[SO42–] – 0.5 [NH4+]) and organic carbon. The highest YdiOS appeared in isoprene SOA and the lowest YdiOS in α-pinene SOA. Under our experimental conditions, more than 50% of the total sulfates in sulfuric acid-seeded isoprene SOA were dialkylsulfates. For all SOA, higher YdiOS was observed under higher NOx conditions (VOC (ppb C)/NO (ppb)<15). Among the major functional groups (–COOH, –CO–H, –CHO and –ONO2) predicted to be present using a simple absorptive partitioning model of organic products in the multiphase system (gas, organic aerosol and inorganic aerosol), the concentrations of –CO–H, –CHO and –ONO2 groups were found to be correlated with YdiOS. In particular, a strong correlation was observed between YdiOS and the concentration of alcohol functional groups.