Peroxy acetyl nitrate (PAN) is a key component of photochemical smog and plays an important role in atmospheric chemistry. Though it has been known that PAN is produced via reactions of nitrogen oxides (NOx) with some volatile organic compounds (VOCs), it is difficult to quantify the contributions of individual precursor species. Here we use an explicit photochemical model – Master Chemical Mechanism (MCM) model – to dissect PAN formation and identify principal precursors, by analyzing measurements made in Beijing in summer 2008. PAN production was sensitive to both NOx and VOCs. Isoprene was the predominant VOC precursor at suburb with biogenic impact, whilst anthropogenic hydrocarbons dominated at downtown. PAN production was attributable to a relatively small class of compounds including NOx, xylenes, trimethylbenzenes, trans/cis-2-butenes, toluene, and propene. MCM can advance understanding of PAN photochemistry to a species level, and provide more relevant recommendations for mitigating photochemical pollution in large cities.

The Community Multi-scale Air Quality modeling system is used to investigate the response of atmospheric visibility to the emission reduction from different sectors (i.e. industries, traffic and power plants) in the Yangtze River Delta, China. Visibility improvement from exclusive reduction of NOx or VOC emission was most inefficient. Sulfate and organic aerosol would rebound if NOx emission was exclusively reduced from any emission sector. The most efficient way to improve the atmospheric visibility was proven to be the multi-pollutant control strategies. Simultaneous emission reductions (20–50%) on NOx, VOC and PM from the industrial and mobile sectors could result in 0.3–1.0 km visibility improvement. And the emission controls on both NOx (85%) and SO2 (90%) from power plants gained the largest visibility improvement of up to 4.0 km among all the scenarios. The seasonal visibility improvement subject to emission controls was higher in summer while lower in the other seasons.

This study analyzes the potential to reduce air pollutants while achieving the 2 °C global temperature change limit target above pre-industrial levels, by using the bottom-up optimization model, AIM/Enduse[Global]. This study focuses on; 1) estimating mitigation potentials and costs for achieving 2 °C, 2.5 °C, and 3 °C target scenarios, 2) assessing co-benefits of reducing air pollutants such as NOx, SO2, BC, PM, and 3) analyzing features of sectoral attributions in Annex I and Non-Annex I groups of countries. The carbon tax scenario at 50 US$/tCO2-eq in 2050 can reduce GHG emissions more than the 3 °C target scenario, but a higher carbon price around 400 US$/tCO2-eq in 2050 is required to achieve the 2 °C target scenario. However, there is also a co-benefit of large reduction potential of air pollutants, in the range of 60–80% reductions in 2050 from the reference scenario while achieving the 2 °C target.

Metro rail has been introduced in Delhi in 2002 to provide alternative mode of public transportation. The introduction of metro rail has resulted in passenger ridership shift from road based transport to metro rail. In order to estimate the emissions (CO, HC, NOx, PM and CO2), metro rail ridership has been converted to equivalent number of on–road vehicles which otherwise would have been playing in the absence of mass rapid transit system. The emission estimation for the year 2006 and 2011 corresponding to the completion of phase I and phase II of Delhi metro rail has been made using emission and deterioration factor(s) for different category and vintage of vehicles. The sensitivity analysis has been carried out to assess the influence of different combination of input parameters such as modal shift, engine technology, and fuel type on emissions. In addition, CO2 emissions saved due to shifting of motor vehicle ridership to metro rail has been estimated and compared with the CO2 produced (off–site) due to electricity consumption by Delhi metro rail for its various operations. The findings indicate that present modal shift scenario does not yield CO2 benefits. However, it is expected that with the increase in metro ridership, changes in modal shift and energy conservation initiatives by Delhi metro, CO2 emission saving could be possible.

Wintertime chemical composition of water–soluble particulate matter with aerodynamic diameter less than 2.5μm (PM2.5) was monitored in the Treasure Valley region near Boise, Idaho. Aerosol was sampled using a Particle Into Liquid Sampler (PILS) and subsequently analyzed using ion exchange chromatography and a total organic carbon analyzer. During the two–month sampling campaign, the region experienced varying meteorological regimes, with an extended atmospheric stagnation event towards the end of the study. For all of the weather regimes, water–soluble PM2.5 was dominated by organic material, but particulate nitrate showed the greatest variation over time. These variations in particulate nitrate concentration were found to be dependent on the time of day, nitrogen oxides (NOX) concentrations, and relative humidity. The increases in particulate nitrate did not correlate with an equivalent molar increase of ammonium concentration, ruling out solid ammonium nitrate formation as the dominant source. Instead, our analysis using an online aerosol thermodynamic model suggests that the condensation of gas phase nitric acid was possible within the meteorological conditions experienced during the study. In running this model, atmospheric chemical and physical parameters close to those observed during the study were used as model input. The simulation was run for three different scenarios, representing the different meteorological regimes experienced during the study. From the simulation particulate nitrate concentration was highest during cold and humid nights. Currently this region is in attainment with the National Ambient Air Quality Standards (NAAQS) for PM2.5; however, with the projected increase in population and economic growth, and the subsequent increase in NOX emissions, these episodic increases in particulate nitrate have the potential of pushing the area to non–attainment status.

Development and urbanization over the past decade has led to rapid increase in the population of Delhi, the metropolitan city of India. Consequently, there has been a tremendous increase in the number of vehicles, which are causing very high levels of air pollution. Vehicular emissions are becoming most predominant source of air pollution in Delhi. An annual emission inventory of road transport emissions of pollutants including carbon monoxide (CO), methane (CH4), nitrogen oxides (NOX), sulfur dioxide (SO2), volatile organic compounds (VOCs), particulate matter (PM10), lead (Pb) and hydrocarbon (HC), organic carbon (OC) and black carbon (BC) has been developed (for the period 2000–2010), for the Delhi region. Emissions have been estimated using emission factor and activity–based approach recommended by IPCC. The emissions of CO and NOX have increased nearly 77% and 29% respectively over 2000 to 2010, whereas contribution of SO2 has greatly reduced (~21%) due to phasing out of diesel driven buses and implementation of Bharat Stage–III norms to commercial vehicles. An appreciable increase in NOX emissions has been observed after 2005, which might be due to the use of CNG fuel. Emissions of PM10, OC and BC have decreased in 2001 and 2002, however these are continuously increasing after 2002 due to rapid rise in the annual rate of growth of registered vehicles in Delhi. Two wheelers (2Ws), which constitute 60% of total registered vehicles, have been found to be major contributors towards emissions of the pollutants considered in the present study.

The purpose of the present work was to study the concentration variations in O3, NO, NO2, NOX over a 4–year period (2006–2009), using the Kolmogorov–Zurbenko filter. Data were decomposed into seasonal and trend components. Seasonal component of the time–series analysis (2006–2009) of NO and NOx in Canoas and Esteio showed values above average during the cold seasons, while O3 showed an opposite pattern. The trend component was marked by the decrease of NO2 at Canoas and the increase of NO at Esteio, thus revealing their variation (NO and NOX) due to local emissions. Furthermore, evaluations of the mean daily concentrations of NO, NOX, NO2, O3, PM10 and CO, and correlations of these pollutants with meteorological parameters (ambient temperature, wind velocity, solar radiation and relative humidity) allowed the confirmation of the influence of mobile sources in the study area.

In the present study, the investigation of the levels of the local and regional oxidants concentration at Athens, Greece, is attempted by analyzing the observations obtained at an urban and a rural station, during 2001–2011 and 2007–2011, respectively. A progressive increase of the daytime and nighttime average of [NO₂]/[Oₓ] versus [NOₓ] is observed showing a larger proportion of Oₓin the form of NO₂when the level of NOₓincreases. Similar results are observed when studying the variation of mean values of [NO₂]/[NOₓ] versus [NOₓ]. The results obtained when compared with those that have earlier detected elsewhere, revealed similarities and discrepancies that are discussed in detail. The parameterized curves that are presented for the first time in this paper may be used by the air quality planners to track the trends in other cities also, and to understand what is or was driving them.

The production of cement in China is accompanied by various emissions, such as fine particulate matter, heavy metals, nitrogen oxides, sulfur oxides, carbon dioxide…. Moreover, cement kiln presents a potential health risk to its surroundings, linking to emissions of persistent organic pollutants (POPs), such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), in brief dioxins. Flue gas samples were collected from five typical cement kilns during twelve runs and were used to evaluate the levels and distribution of PCDD/Fs in the emissions from cement kilns. The PCDD/Fs concentrations (136 congeners) and I-TEQ values ranged from 2.3 to >40 ng/m³and 9.3 ∼ 90.8 × 10⁻³ ng I-TEQ/m³, respectively, which were lower than the emission standard in China (0.1 ng I-TEQ/m³). In weight units, the dominant congeners were OCDD, 1,2,3,4,6,7,8-HpCDF, and OCDF; 2,3,4,7,8-PeCDF is the largest contributor (36–66 %) to the total I-TEQ value of twelve runs. HxCDF and TCDF were the first two most abundant homologue groups (12–85 and 4–52 %), and the homologue concentration decreased with rising chlorine number for PCDDs. In addition, there was no marked difference in homologue profiles when solid wastes (refuse-derived fuel and municipal solid waste) and hazardous wastes (DDT and POPs) were combusted as supplemental fuels. The use of various supplemental fuels had no obvious effect on the fingerprint of PCDD/F homologues. Moreover, there was no significant difference in levels of PCDD/Fs emission due to the diversity of production capacity, which were consistent with reported previously. Air pollution control device had effect on the homologue profiles, and cement system with electrostatic precipitators (ESP) had more fractions of octachloro congeners to the total.

Concentrations and chemical composition of the coarse particle fraction (PMc) were investigated at two urban sites in the city of Thessaloniki, Greece, through concurrent sampling of PM₁₀ and PM₂.₅ during the warm and the cold months of the year. PMc levels at the urban-traffic site (UT) were among the highest found in literature worldwide exhibiting higher values in the cold period. PMc levels at the urban-background site (UB) were significantly lower exhibiting a reverse seasonal trend. Concentration levels of minerals and most trace metals were also higher at the UT site suggesting a stronger impact from traffic-related sources (road dust resuspension, brake and tire abrasion, road wear). According to the chemical mass closure obtained, minerals (oxides of Si, Al, Ca, Mg, Fe, Ti, and K) dominated the PMc profile, regardless of the site and the period, with organic matter and secondary inorganic aerosols (mainly nitrate) also contributing considerably to the PMc mass, particularly in the warm period. The influence of wind speed to dilution and/or resuspension of coarse particles was investigated. The source of origin of coarse particles was also investigated using surface wind data and atmospheric back-trajectory modeling. Finally, the contribution of resuspension to PMc levels was estimated for air quality management perspectives.