Bernhard Rappenglück

Quasi-continuous measurements of non-methane hydrocarbons (NMHC) in the Greater Athens area during medcaphot-trace

Abstract During the comprehensive field campaign MECAPHOT-TRACE (20 August to 20 September 1994) quasi-continuous measurements of NMHC in the range of C 4 –C 12 were carried out for the first time in the Greater Athens area simultaneously at two sites, by means of on-line gas-chromatographic methods. The results show a heavy load of hydrocarbons in ambient air, especially during stagnant weather conditions that favour the development of land–sea-breeze circulations. Overall the urban hydrocarbon mix reflects the emission of traffic. This influence is confirmed through correlation analyses of hydrocarbon ratios, especially aromatic compound ratios, and their dependence on both wind direction and wind velocity at a suburban receptor site. The ethylbenzene/ m -xylene-ratio turned out to be a good indicator for the impact of anthropogenically related hydrocarbon chemistry leading to the formation of secondary pollutants. Episodes will be discussed that elucidate the importance of hydrocarbons in the course of ozone formation.

An analysis of the vertical structure of the atmosphere and the upper‐level meteorology and their impact on surface ozone levels in Houston, Texas

[1] Despite emission reductions, Houston continues to be designated as a nonattainment area for ozone (O 3 ) by the Environmental Protection Agency. Upper-level synoptic maps and information about the vertical structure of the lower troposphere obtained by in situ measurements were analyzed to characterize ozone exceedances in which peak 8-h average concentration exceeded 85 ppb during the Texas Air Quality Study-II in August-September 2006. Cluster analysis of meteorological conditions showed that the highest background surface O 3 concentrations occurred under northerly or easterly flow regimes at 850 hPa, coinciding with the advection of dry continental air. Exceedance days in September 2006 occurred almost exclusively in postfrontal environments. These frontal passages are associated with shifts in wind direction and may lead to increases in background O 3 from 30 ppbv (marine) to 60-70 ppbv (continental) throughout the lower troposphere. Several factors are identified to be important for 8-h average ozone peaks in Houston under well-developed land-sea-bay breeze conditions, including (1) the presence of easterly winds advecting industrial emissions from the Ship Channel, and (2) the presence of persistent large-scale northerly flows aloft advecting elevated continental background ozone levels that are eventually entrained into lower layers through the growth of the convective planetary boundary layer.

The Evolution of Photochemical Smog in the Metropolitan Area of Santiago de Chile

In November and December 1996 the PHOTOCHEMICAL CAMPAIGN took place in the Metropolitan Area of Santiago de Chile and covered a range of simultaneous measurements of meteorological parameters and air chemical compounds, including ozone, carbon monoxide, nitrogen oxides, peroxyacetyl nitrate (PAN), and online nonmethane hydrocarbons (NMHC) in the range of C4‐C12. Measurements were obtained at a downtown site and a receptor site. In addition to high ozone concentrations, Santiago faces high PAN values that can reach to more than 20 ppbv. It is estimated that more than 50% of the daytime maximum of ozone and almost all PAN are formed within the urban plume. Ozone : PAN ratios for diurnal maxima were about 7.7. The behavior of PAN is linked strongly to anthropogenic species, especially aromatic compounds, whereas biogenic NMHC also may contribute to afternoon ozone concentrations. The ethylbenzene : m-xylene ratio can be used as a good indicator for the effect of anthropogenically related hydrocarbon chemical reactions that lead to the formation of secondary pollutants. Using this ratio, mixing ratios for hydroxyl radical (OH) were calculated. Mean diurnal maximum OH mixing ratios were about 2.9 3 106 molecules per centimeter cubed.

Deciphering the role of radical precursors during the Second Texas Air Quality Study.

Abstract The Texas Environmental Research Consortium (TERC) funded significant components of the Second Texas Air Quality Study (TexAQS II), including the TexAQS II Radical and Aerosol Measurement Project (TRAMP) and instrumented flights by a Piper Aztec aircraft. These experiments called attention to the role of short-lived radical sources such as formaldehyde (HCHO) and nitrous acid (HONO) in increasing ozone productivity. TRAMP instruments recorded daytime HCHO pulses as large as 32 parts per billion (ppb) originating from upwind industrial activities in the Houston Ship Channel, where in situ surface monitors detected HCHO peaks as large as 52 ppb. Moreover, Ship Channel petrochemical flares were observed to produce plumes of apparent primary HCHO. In one such combustion plume that was depleted of ozone by large emissions of oxides of nitrogen (NOx), the Piper Aztec measured a ratio of HCHO to carbon monoxide (CO) 3 times that of mobile sources. HCHO from uncounted primary sources or ozonolysis of underestimated olefin emissions could significantly increase ozone productivity in Houston beyond previous expectations. Simulations with the CAMx model show that additional emissions of HCHO from industrial flares or mobile sources can increase peak ozone in Houston by up to 30 ppb. Other findings from TexAQS II include significant concentrations of HONO throughout the day, well in excess of current air quality model predictions, with large nocturnal vertical gradients indicating a surface or near-surface source of HONO, and large concentrations of nighttime radicals (∼30 parts per trillion [ppt] HO2). HONO may be formed heterogeneously on urban canopy or particulate matter surfaces and may be enhanced by organic aerosol of industrial or motor vehicular origin, such as through conversion of nitric acid (HNO3). Additional HONO sources may increase daytime ozone by more than 10 ppb. Improving the representation of primary and secondary HCHO and HONO in air quality models could enhance the simulated effectiveness of control strategies.

Nonmethane hydrocarbons (NMHC) in the Greater Munich Area/Germany

Abstract During several field campaigns in the years 1993–1997 quasi-continuous measurements of NMHC data were obtained at various locations (urban/suburban/rural) within the Greater Munich Area (GMA) by means of on-line gaschromatographic methods. Though limited to NMHC between C6 and C9 it comprises the first comprehensive data base for this region that features high temporal resolution. The results for the downtown area show relatively low NMHC values compared to other cities worldwide. Propene-eqivalent analysis suggests that aromatic compounds such as toluene and m & p-xylenes play a major role in the formation of urban photochemical smog in the GMA. Since aromatic compounds were found to be ubiquitous at all measurement sites (altogether 8 sites) the pattern of these NMHC were investigated thoroughly. The results suggest that aromatic compounds are most effective in the urban/rural transition zone where VOC-limitation of ozone formation can be expected.

Measurements of ozone and peroxyacetyl nitrate (pan) in Munich

Simultaneous measurements of ozone and —for the first time in Munich—of PAN were carried out at two sites in the urban area of Munich during two periods (16 June–15 September 1989 and 1 January–30 April 1990). Maximum mixing ratios reached 75 ppbv for ozone (10-min-average) and 5.6 ppbv for PAN (20-min-value), respectively. Ozone showed more pronounced diurnal variations than PAN. In both cases they were related to diurnal variations of the global radiation and the mixing ratios of NOx. Regarding ozone linear correlation analysis with meteorological parameters revealed distinct dependencies, especially on UV radiation, whereas the results for PAN reflected its more complicated formation. As far as dependencies on wind velocity are concerned, both ozone and PAN exhibited maximum mixing ratios in cases where the wind velocity was below 5 ms−1. With increasing wind velocity both mixing ratios tended towards their natural background concentrations. Investigations concerning the influence of the wind direction did not disclose any particular local effects, but rather a relationship to the general weather situations. On the whole, PAN could be considered as a more characteristics indicator of smog conditions than ozone due to its low background concentrations and its thermal instability.

Formaldehyde columns from the Ozone Monitoring Instrument: Urban versus background levels and evaluation using aircraft data and a global model

GEOS‐Chem, within expected uncertainty for the retrieval. Some negative bias is expected for the satellite and model, given the plume sampling of many flights and averaging over the satellite and model footprints. Major axis regression for OMI versus aircraft and model columns yields slopes (95% confidence intervals) of 0.80 (0.62–1.03) and 0.98 (0.73–1.35), respectively, with no significant intercept. Aircraft measurements indicate that the normalized vertical HCHO distribution, required by the satellite retrieval, is well captured by GEOS‐Chem, except near Mexico City. Using measured HCHO profiles in the retrieval algorithm does not improve satellite‐aircraft agreement, suggesting that use of a global model to specify shape factors does not substantially degrade retrievals over polluted areas. While the OMI measurements show that biogenic volatile organic compounds dominate intra‐annual and regional WHCHO variability across the United States, smaller anthropogenic WHCHO gradients are detectable at finer spatial scales (∼20–200 km) near many urban areas.

Radical precursors and related species from traffic as observed and modeled at an urban highway junction

Nitrous acid (HONO) and formaldehyde (HCHO) are important precursors for radicals and are believed to favor ozone formation significantly. Traffic emission data for both compounds are scarce and mostly outdated. A better knowledge of todays HCHO and HONO emissions related to traffic is needed to refine air quality models. Here the authors report results from continuous ambient air measurements taken at a highway junction in Houston, Texas, from July 15 to October 15, 2009. The observational data were compared with emission estimates from currently available mobile emission models (MOBILE6; MOVES [MOtor Vehicle Emission Simulator]). Observations indicated a molar carbon monoxide (CO) versus nitrogen oxides (NOx) ratio of 6.01 ± 0.15 (r 2 = 0.91), which is in agreement with other field studies. Both MOBILE6 and MOVES overestimate this emission ratio by 92% and 24%, respectively. For HCHO/CO, an overall slope of 3.14 ± 0.14 g HCHO/kg CO was observed. Whereas MOBILE6 largely underestimates this ratio by 77%, MOVES calculates somewhat higher HCHO/CO ratios (1.87) than MOBILE6, but is still significantly lower than the observed ratio. MOVES shows high HCHO/CO ratios during the early morning hours due to heavy-duty diesel off-network emissions. The differences of the modeled CO/NOx and HCHO/CO ratios are largely due to higher NOx and HCHO emissions in MOVES (30% and 57%, respectively, increased from MOBILE6 for 2009), as CO emissions were about the same in both models. The observed HONO/NOx emission ratio is around 0.017 ± 0.0009 kg HONO/kg NOx which is twice as high as in MOVES. The observed NO2/NOx emission ratio is around 0.16 ± 0.01 kg NO2/kg NOx, which is a bit more than 50% higher than in MOVES. MOVES overestimates the CO/CO2 emission ratio by a factor of 3 compared with the observations, which is 0.0033 ± 0.0002 kg CO/kg CO2. This as well as CO/NOx overestimation is coming from light-duty gasoline vehicles. Implications: Nitrous acid (HONO) and formaldehyde (HCHO) are important precursors for radicals that ultimately contribute to ozone formation. There still exist uncertainties in emission sources of HONO and HCHO and thus regional air quality modeling still tend to underestimate concentrations of free radicals in the atmosphere. This paper demonstrates that the latest U.S. Environmental Protection Agency (EPA) traffic emission model MOVES still shows significant deviations from observed emission ratios, in particular underestimation of HCHO/CO and HONO/NOx ratios. Improving the performance of MOVES may improve regional air quality modeling.

Overview of the SHARP campaign: Motivation, design, and major outcomes

The Study of Houston Atmospheric Radical Precursors (SHARP) was a field campaign developed by the Houston Advanced Research Center on behalf of the Texas Environmental Research Consortium. SHARP capitalized on previous research associated with the Second Texas Air Quality Study and the development of the State Implementation Plan (SIP) for the Houston-Galveston-Brazoria (HGB) ozone nonattainment area. These earlier studies pointed to an apparent deficit in ozone production in the SIP attainment demonstration model despite the enhancement of simulated emissions of highly reactive volatile organic compounds in accordance with the findings of the original Texas Air Quality Study in 2000. The scientific hypothesis underlying the SHARP campaign was that there are significant undercounted primary and secondary sources of the radical precursors, formaldehyde, and nitrous acid, in both heavily industrialized and more typical urban areas of Houston. These sources, if properly taken into account, could increase the production of ozone in the SIP model and the simulated efficacy of control strategies designed to bring the HGB area into ozone attainment. This overview summarizes the precursor studies and motivations behind SHARP, as well as the overall experimental design and major findings of the 2009 field campaign. These findings include significant combustion sources of formaldehyde at levels greater than accounted for in current point source emission inventories; the underestimation of formaldehyde and nitrous acid emissions, as well as CO/NOx and NO2/NOx ratios, by mobile source models; and the enhancement of nitrous acid by atmospheric organic aerosol.

Emission measurements of alkenes, alkanes, SO2, and NO2 from stationary sources in Southeast Texas over a 5 year period using SOF and mobile DOAS

A mobile platform for flux measurements of VOCs (alkanes and alkenes), SO2, and NO2 emissions using the Solar Occultation Flux (SOF) method and mobile differential optical absorption spectroscopy (DOAS) was used in four different studies to measure industrial emissions. The studies were carried out in several large conglomerates of oil refineries and petrochemical industries in Southeast and East Texas in 2006, 2009, 2011, and 2012. The measured alkane emissions from the Houston Ship Channel (HSC) have been fairly stable between 2006 and 2011, averaging about 11,500kg/h, while the alkene emissions have shown greater variations. The ethene and propene emissions measured from the HSC were 1511kg/h and 878kg/h, respectively, in 2006, while dropping to roughly 600kg/h for both species in 2009 and 2011. The results were compared to annual inventory emissions, showing that measured VOC emissions were typically 5-15 times higher, while for SO2 and NO2 the ratio was typically 0.5-2. AP-42 emission factors were used to estimate meteorological effects on alkane emissions from tanks, showing that these emissions may have been up to 35-45% higher during the studies than the annual average. A more focused study of alkene emissions from a petrochemical complex in Longview in 2012 identified two upset episodes, and the elevation of the total emissions during the measurement period due to the upsets was estimated to be approximately 20%. Both meteorological and upset effects were small compared to the factor of 5-15, suggesting that VOC emissions are systematically and substantially underestimated in current emission inventories.