Remote Aerosol Simulated During the Atmospheric Tomography (ATom) Campaign and Implications for Aerosol Lifetime

We investigate and assess how well a global chemical transport model (GEOS-Chem) simulates submicron aerosol mass concentrations in the remote troposphere. The simulated speciated aerosol (organic aerosol (OA), black carbon, sulfate, nitrate, and ammonium) mass concentrations are evaluated against airborne observations made during all four seasons of the NASA Atmospheric Tomography Mission (ATom) deployments over the remote Pacific and Atlantic Oceans. Such measurements over pristine environments offer fresh insights into the spatial (Northern [NH] and Southern Hemispheres [SH], Atlantic, and Pacific Oceans) and temporal (all seasons) variability in aerosol composition and lifetime, away from continental sources. The model captures the dominance of fine OA and sulfate aerosol mass concentrations in all seasons. There is a high bias across all species in the ATom-2 (NH winter) simulations; implementing recent updates to the wet scavenging parameterization improves our simulations, eliminating the large ATom-2 (NH winter) bias, improving the ATom-1 (NH summer) and ATom-3 (NH fall) simulations, but producing a model underestimate in aerosol mass concentrations for the ATom-4 (NH spring) simulations. Following the wet scavenging updates, simulated global annual mean aerosol lifetimes vary from 1.9 to 4.0 days, depending on species. Aerosol lifetimes in each hemisphere vary by season, and are longest for carbonaceous aerosol during the southern hemispheric fire season. The updated wet scavenging parameterization brings simulated concentrations closer to observations and reduces global aerosol lifetime for all species, indicating the sensitivity of global aerosol lifetime and burden to wet removal processes.

Monetary quantification of COVID-19 impacts on sustainable development goals: Focus on air pollution and climate change

COVID-19 epidemic struck without warning, wreaking havoc on all aspects of society. The chapter discusses the quantification of impacts of COVID-19-induced control strategies and restricted resource consumption on sustainable development goals (SDGs), focusing on SDG-3 (Good Health and Wellbeing) and SDG-13 (Climate Action). The impacts of reduced PM_2.5 emission are monitored using moderate resolution imaging spectroradiometer (MODIS) satellite data for India (2020–21) and the reduction in the morbidity and mortality is valued using the cost of illness (COI), disability-adjusted life years (DALY), and value of statistical life (VSL). The reported reduction of CO₂e emissions of about 40% during the year, in the cities, is quantified for the country and monetized using the regional values of the social cost of carbon (SCC). The chapter also lays a framework for quantifying and valuing such impacts related to other SDGs and can be used by policymakers for implementation and quantified decision-making.

Variations in physicochemical properties of airborne particles during a heavy haze-to-dust episode in Beijing

The variations in physicochemical properties of airborne particles collected during a typical transition from haze to dust were investigated using single particle analysis with transmission and scanning electron microscopes combined with online measurement of chemical compositions of airborne particles in Beijing in February 2013. The transition was divided into three phases based on the weather condition. During haze pollution (Phase 1), gaseous and particle pollutants enhanced gradually. Results from single particle analysis showed that more coatings and more anthropogenic elements (e.g., S) appeared on the surface of fine and coarse particles, which was probably caused by efficient aqueous-phase reactions under high humidity (70%) condition. Phase 2 was dust intrusion episode. PM₁₀ reached over 1000 μg m^-3. Larger fractions of mineral particles and bare-like soot particles were observed in fine particles, while the fraction of secondary particles with coatings decreased. The proportion of black carbon in submicron particles also increased. Photochemical oxidation in gas phase likely dominated in secondary formation under high O₃ concentration. After the dust episode (Phase 3), secondary formation enhanced obviously. Soot aged quickly and had a larger mode of 0.45 μm than the other phases. The size modes of airborne fine particles during Phases 1 and 3 were 0.35 μm, which were a bit larger than that during Phase 2 (0.24 μm). These results indicate that dust plumes accompanied with strong wind brought mineral particles in both fine and coarse modes and freshly emitted particles with smaller sizes, and swept away pre-presence air pollutants. This study could provide detailed information on the physicochemical properties of airborne particles during typical severe pollution processes in a short time. Such short-term change should be taken into account in order to more accurately assess the environmental, climatic and health-related effects of airborne particles.

Improved parameterization of dust emission (PM10) fluxes by the gradient method using the Naiman tower data at the Horqin desert in China

Dust emission/deposition flux has been estimated using the gradient method with the two-level (3 and 15m high) measured PM(10) concentrations and the sonic anemometer measured momentum and kinematic heat fluxes at 8m high from a 20-m monitoring tower located at Naiman (Horqin desert) in the Asian dust source region in China for the winter of November 2007 to March 2008. The time series of measured PM(10) concentration at 3m high is used to identify the dust event and the non-dust event periods. It is found that the dust emission/deposition flux (F(C)) shows a significant diurnal variation with the maximum emission flux of 5.8 kg km(-2)h(-1) at noon and the minimum of -1.6 kg km(-2)h(-1) in the afternoon for the non-dust event cases. Whereas for the dust event cases, the dust emission flux is found to occur when the prevailing winds are westerlies to northerlies with the maximum flux of 1275 kg km(-2)d(-1), while the maximum dust deposition flux of 148 kg km(-2)d(-1) occurs with the prevailing winds of southerlies to easterlies without any diurnal variation. The optimal regression equation between F(C) and the friction velocity (u(*)) for the dust emission cases is found to be F(C)=9.55 u(*)(3.13) with the R(2) value of 0.73. However, this regression equation can be improved by taking into account the convective velocity (w(*)). The resulting optimal regression equation is found to be F(C)=9.3(u(*)-0.1w(*))(3.19) for the stable stratification (w(*)<0) with the R(2) value of 0.77 and F(C)=10.5(u(*)+0.34w(*))(4.11) for the unstable stratification (w(*)>0) with the R(2) value of 0.78, suggesting the importance of the convective velocity on the dust emission flux.

A parameterization of dust concentration (PM₁₀) of dust events observed at Erdene in Mongolia using the monitored tower data

Hourly mean time series of dust concentration (PM₁₀) measured at 3m high and a sonic-anemometer measured momentum and kinematic heat fluxes at 8m high above the surface have been obtained from a 20-m monitoring tower located at Erdene in the Asian dust source region of Mongolia for years of 2009 and 2010. These time series were used to identify dust events and to develop optimal regression equations for the dust concentration of dust events with the friction velocity (u(*)) and the convective velocity scale (w(*)). In total, 68 dust events were identified in 2009 (except for November) and 43 dust events for the period from March to August in 2010. The duration of each dust event ranged from 3-29 h in 2009 and 5-35 h in 2010. The maximum hourly mean dust concentration of the dust event was found to be 4,107 μg m⁻³ in May in 2009 and 4,708 μg m⁻³ in March in 2010 while a minimum of 251 μg m⁻³ in August in 2009 and 662 μg m⁻³ in June in 2010. The optimal regression equation for the dust concentration (C) of dust events was found to have the form of log C=a+b(u(*)+cw(*))(n), where a, b, c and n are constants that vary month to month. The convective velocity scale (w(*)) that has not been taken into account in most dust modelings was found to enhance the dust concentration of dust events during the cold period from December to March when the soil temperature was below the freezing level for both the stable (w(*)<0) and unstable (w(*)>0) stratifications, whereas the convective velocity caused a reduction in the dust concentrations during the warm period from April to October, suggesting the importance of the convective velocity to estimate dust concentration of dust events.

Estimates of Asian dust deposition over the Asian region by using ADAM2 in 2007

The Asian Dust Aerosol Model 2 (ADAM2) with the MM5 meteorological model has been employed to estimate the dust concentration, and wet and dry depositions of dust in the Asian region for the year of 2007. It is found that the model simulates quite reasonably the dust (PM(10)) concentrations both in the dust source region (100-110 degrees E and 37-43 degrees N) and the downstream region of Korea. The starting and ending times of most of dust events and their peak concentration occurring times are well simulated. The annual average dust (PM(10)) concentration near the surface is found to be 171microgm(-3) over the dust source area, 39microgm(-3) over the Yellow Sea, 25microgm(-3) over the Korean peninsula and 17microgm(-3) over the East Sea. It is also found that the annual total deposition of dust is about 118.1tkm(-2) (dry deposition, 101.4tkm(-2); wet deposition, 16.7tkm(-2)) in the dust source region, 19.0tkm(-2) (dry deposition, 7.8tkm(-2); wet deposition, 11.2tkm(-2)) in the Yellow Sea, 12.6tkm(-2) (dry deposition, 6.5tkm(-2); wet deposition, 6.1tkm(-2)) in the Korean peninsula and 10.7tkm(-2) (dry deposition, 2.1tkm(-2); wet deposition, 8.6tkm(-2)) in the East Sea. Their ratios of wet deposition to total deposition of dust in the respective regions are 14%, 59%, 48% and 80%. This clearly indicates that the main dust removal mechanism from the atmosphere is dry deposition over the source region whereas wet deposition predominates in the downstream region of the sea. The estimated dust deposition could adversely impact the eco-environmental system in the downstream regions of the dust source region significantly.

Particulate air pollution in Lanzhou China

Concentrations of total suspended particles (TSP) and PM(10) in Lanzhou China have been kept high for the past two decades. Data collected during the intensive observational period from October 1999 to April 2001 show high TSP and PM(10) concentrations. Starting from November, the PM(10) pollution intensifies, and reaches mid to high alert level of air pollution, continues until April next year, and is at low alert level in the summer. In the winter and spring, the TSP concentration is 2-10 times higher than the third-level criterion of air quality (severe pollution). Effects of intrinsic factors (sources of pollution) and remote preconditions (propagation of dust storms) for severe PM(10) and TSP pollution in Lanzhou are analyzed.

Intercontinental transport of aerosols and photochemical oxidants from Asia and its consequences

The intercontinental transport of aerosols and photochemical oxidants from Asia is a crucial issue for air quality concerns in countries downwind of the significant emissions and concentrations of pollutants occurring in this important region of the world. Since the lifetimes of some important pollutants are long enough to be transported over long distance in the troposphere, regional control strategies for air pollution in downwind countries might be ineffective without considering the effects of long-range transport of pollutants from Asia. Field campaigns provide strong evidence for the intercontinental transport of Asian pollutants. They, together with ground-based observations and model simulations, show that the air quality over parts of North America is being affected by the pollutants transported from Asia. This paper examines the current understanding of the intercontinental transport of gases and aerosols from Asia and resulting effects on air quality, and on the regional and global climate system.

Spectroscopic analysis of iron-oxide minerals in aerosol particles from northern China

Diffuse reflectance spectrometry was used to study iron-oxide minerals and to investigate the reflectance characteristics of eolian dust collected during the spring of 2001 and 2002 on bulk filters from three sites in northern China. The first derivatives of the reflectance spectra were consistent with signals from two iron-oxide minerals, hematite and goethite, at wavelengths of 565 and 435 nm, respectively, and these values varied with the iron concentrations in the samples. The percent reflectances for the yellow, orange and red bands increased with the iron concentrations and with the first derivative values representing hematite and goethite while those for violet, blue and green bands decreased correspondingly. The results show that iron-oxide minerals play an important role in determining the aerosol particles' color and reflectance properties. Moreover, the relative amounts of the two iron-oxides in Asian dust apparently differ from those in African dust, suggesting that the iron-oxides may provide another tool for tracing the origins of eolian dust on a global scale.

Global air pollution crossroads over the Mediterranean

The Mediterranean Intensive Oxidant Study, performed in the summer of 2001, uncovered air pollution layers from the surface to an altitude of 15 kilometers. In the boundary layer, air pollution standards are exceeded throughout the region, caused by West and East European pollution from the north. Aerosol particles also reduce solar radiation penetration to the surface, which can suppress precipitation. In the middle troposphere, Asian and to a lesser extent North American pollution is transported from the west. Additional Asian pollution from the east, transported from the monsoon in the upper troposphere, crosses the Mediterranean tropopause, which pollutes the lower stratosphere at middle latitudes.