Non-Stationarity of Aerosol Extinction Coefficient per Unit of Mass in Autumn and Winter in Chengdu, China

Based on hourly observation data from the aethalometer and GRIMM180 environment particle monitor as well as the simultaneous data of visibility (V), relative humidity (RH) and nitrogen dioxide (NO2) from October to December in 2017 in Chengdu, the corresponding time series of aerosol extinction coefficient per unit of mass is retrieved. The generalized additive models (GAMs) are adopted to analyze the non-stationarity of the time series of aerosol extinction coefficient per unit of mass and to explore the responses of the aerosol extinction coefficient per unit of mass to the aerosol component structure factors (ρBC/ρPM10, ρPM1/ρPM2.5, ρPM1~2.5/ρPM2.5 and ρPM2.5/ρPM10; ρ represents particle mass concentration) and RH. The results show that through the comparative analysis of stationary and non-stationary models, the time series of aerosol extinction coefficient per unit of mass in autumn and winter in Chengdu is non-stationary. In addition, the RH and aerosol component structure factors are all significant nonlinear covariates that affect the non-stationarity of the aerosol extinction coefficient per unit of mass. According to the influence of covariates, the sequence is as follows: RH > ρBC/ρPM10 > ρPM2.5/ρPM10 > ρPM1/ρPM2.5. At PM2.5 pollution concentration (ρPM2.5 > 75 μg m−3), according to the influence of covariates, the sequence is as follows: RH > ρPM1~2.5/ρPM2.5 > ρBC/ρPM10 > ρPM2.5/ρPM10. Moreover, the interaction between RH and aerosol component structure factors significantly affects the aerosol extinction coefficient per unit of mass. The condition of high RH, high ρPM2.5/ρPM10, high ρPM1/ρPM2.5 and low ρBC/ρPM10 has a synergistic amplification effect on the increase of the aerosol extinction coefficient per unit of mass. At PM2.5 pollution concentration, the synergistic effect of high RH, high ρPM2.5/ρPM10, high ρPM1~2.5/ρPM2.5 and low ρBC/ρPM10 is beneficial to the increase of the aerosol extinction coefficient per unit of mass.

Formation mechanisms of nitrous acid (HONO) during the haze and non-haze periods in Beijing, China

As an important precursor of hydroxyl radical (OH), nitrous acid (HONO) plays a significant role in atmospheric chemistry. Here, an observation of HONO and relevant air pollutants in an urban site of Beijing from 14 to 28 April, 2017 was performed. Two distinct peaks of HONO concentrations occurred during the observation. In contrast, the concentration of particulate matter in the first period (period Ⅰ) was significantly higher than that in the second period (period Ⅱ). Comparing to HONO sources in the two periods, we found that the direct vehicle emission was an essential source of the ambient HONO during both periods at night, especially in period Ⅱ. The heterogeneous reaction of NO₂ was the dominant source in period Ⅰ, while the homogeneous reaction of NO with OH was more critical source at night in period Ⅱ. In the daytime, the heterogeneous reaction of NO₂ was a significant source and was confirmed by the good correlation coefficients (R²) between the unknown sources (P_unknown) with NO₂, PM_2.5, NO₂ × PM_2.5 in period Ⅰ. Moreover, when solar radiation and OH radicals were considered to explore unknown sources in the daytime, the enhanced correlation of P_unknown with photolysis rate of NO₂ and OH ( [Formula: see text]  × OH) were 0.93 in period Ⅰ, 0.95 in period Ⅱ. These excellent correlation coefficients suggested that the unknown sources released HONO highly related to the solar radiation and the variation of OH radicals.

The different sensitivities of aerosol optical properties to particle concentration, humidity, and hygroscopicity between the surface level and the upper boundary layer in Guangzhou, China

This study investigates the impact of aerosol liquid water content (ALWC) and related factors, i.e., relative humidity (RH), aerosol mass concentration (PM_2.5), and aerosol hygroscopicity, on aerosol optical properties, based on field measurements made in the Pearl River Delta (PRD) region of China at the surface (1 November 2019 to 21 January 2020) and in the upper boundary layer (the 532-m Guangzhou tower from 1 February to 21 March 2020). In general, temporal variations in the ambient aerosol backscattering coefficient (β_p) and ALWC followed each other. However, the surface β_p and 532-m β_p had generally opposite diurnal variation patterns, caused by dramatic differences in PM_2.5 and ambient RH between the surface and the upper boundary layer. The ambient 532-m RH was systematically higher than the surface RH, with the latter having a much pronounced diurnal cycle than the former. The surface PM_2.5 concentration was systematically higher than the PM_2.5 concentration at 532 m, and their diurnal cycle patterns were overall opposite. These dramatic differences reveal that the atmospheric variables, i.e., ambient RH and the PM_2.5 concentration in the upper boundary layer, cannot be directly represented by the same variables at the surface. Vertical variability should be considered. Clear differences in the sensitivities of aerosol light scattering to ambient RH, PM_2.5, and aerosol hygroscopicity between the two levels were found and examined. Aerosol chemical composition played a minor role in causing the differences between the two levels. In particular, β_p was more sensitive to PM_2.5 at the surface level but more to the ambient RH in the upper boundary layer. The larger contribution of aerosol loading to the variability in β_p at the surface implies that local emission controls can decrease β_p and further improve atmospheric visibility effectively at the surface during winter in the PRD region.

Filter-based absorption enhancement measurement for internally mixed black carbon particles over southern China

The effect of the mixing state of black carbon (BC) on light absorption is of enduring interest due to its close connection to regional/global climate. Herein, we present concurrent measurements of both BC absorption enhancement (E_abs) and the chemical mixing state in southern China. E_abs was obtained by simultaneous measuring the light absorption coefficient using an aethalometer before and after being heated. The observed E_abs was categorized into non- (E_abs ≤ 1.0), slight (1.0 < E_abs ≤ 1.2), and higher (E_abs > 1.2) enhancement groups, and it was compared to the mixing state of elemental carbon (EC) particles detected by a single particle aerosol mass spectrometer (SPAMS). The individual EC-containing particles were classified into four types, including EC with sodium and potassium ion peaks (NaK-EC), long EC cluster ions (C_n^+/-, n ≥ 6) with sulfate (EC-Sul1), short EC cluster ions (C_n^+/-, n < 6) with sulfate (EC-Sul2), and EC with OC and sulfate (ECOC-Sul). NaK-EC and EC-Sul2 are the dominant EC types. Slight enhancement group is mainly explained by the photochemical production of ammonium sulfate and organics on EC-Sul2 during afternoon hours. In contrast, the higher E_abs is primarily attributed to the enhanced mixing of ammonium chloride with NaK-EC during morning hours, without photochemistry. The characterization of source emissions indicates that NaK-EC is likely from coal combustion and is associated with a relatively higher amount of ammonium chloride. To our knowledge, this is the first report to state that EC particles associated with ammonium chloride have a relatively higher E_abs.

Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN): integrated analysis and intensive winter campaign 2018

Fine-particle pollution associated with winter haze threatens the health of more than 400 million people in the North China Plain. The Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN) investigated the physicochemical mechanisms leading to haze formation with a focus on the contributions of multiphase processes in aerosols and fogs. We integrated observations on multiple platforms with regional and box model simulations to identify and characterize the key oxidation processes producing sulfate, nitrate and secondary organic aerosols. An outdoor twin-chamber system was deployed to conduct kinetic experiments under real atmospheric conditions in comparison to literature kinetic data from laboratory studies. The experiments were spanning multiple years since 2017 and an intensive field campaign was performed in the winter of 2018. The location of the site minimizes fast transition between clean and polluted air masses, and regimes representative for the North China Plain were observed at the measurement location in Gucheng near Beijing. The consecutive multi-year experiments document recent trends of PM_2.5 pollution and corresponding changes of aerosol physical and chemical properties, enabling in-depth investigations of established and newly proposed chemical mechanisms of haze formation. This study is mainly focusing on the data obtained from the winter campaign 2018. To investigate multiphase chemistry, the results are presented and discussed by means of three characteristic cases: low humidity, high humidity and fog. We find a strong relative humidity dependence of aerosol chemical compositions, suggesting an important role of multiphase chemistry. Compared with the low humidity period, both PM₁ and PM_2.5 show higher mass fraction of secondary inorganic aerosols (SIA, mainly as nitrate, sulfate and ammonium) and secondary organic aerosols (SOA) during high humidity and fog episodes. The changes in aerosol composition further influence aerosol physical properties, e.g., with higher aerosol hygroscopicity parameter κ and single scattering albedo SSA under high humidity and fog cases. The campaign-averaged aerosol pH is 5.1 ± 0.9, of which the variation is mainly driven by the aerosol water content (AWC) concentrations. Overall, the McFAN experiment provides new evidence of the key role of multiphase reactions in regulating aerosol chemical composition and physical properties in polluted regions.

Light absorption enhancement of particulate matters and their source apportionment over the Asian continental outflow site and South Yellow Sea

Light absorption enhancement of black carbon due to the aerosol mixing states is an important parameterization for climate modeling, while emission source contributions to the enhancement factor are unclear. An intensive campaign was conducted simultaneously at a China coastal site (Qingdao city) and maritime sites (South Yellow Sea, SYS) in August and Nov to Dec 2018. The absorption enhancement (E_MAC) of the black carbon was calculated using a two-step solvent dissolution protocol and found 1.96 ± 0.68, 1.64 ± 0.38, and 2.40 ± 0.76 for Qingdao summer (QS), Qingdao autumn (QA), and SYS, respectively. Positive matrix factorization (PMF) model identified six sources of PM_2.5 and E_MAC, which were secondary aerosol (with contribution 27.9% and 29.2%), coal combustion (24.9% and 20.2%), industrial emissions (15.2% and 25.4%), sea salt (6.9% and 9.6%), vehicle emissions (12.1% and 10.9%), and soil dust (13.0% and 4.7%), respectively. These sources increased the absorption of black carbon by a factor of 1.25 ± 0.11 (secondary aerosol), 1.21 ± 0.20 (industrial emissions), 1.17 ± 0.08 (coal combustion), 1.09 ± 0.07 (vehicle emissions), 1.08 ± 0.17 (sea salt), and 1.04 ± 0.10 (soil dust). Based on the correlation between PM and E_MAC source contributions, we estimated that secondary aerosols, industrial emissions, and coal combustion contributed to 74.8% of absorption enhancement at a regional scale in China. The source apportionment for E_MAC offers a new diagnosis for each source regarding aerosol forcing simulation which inputs from the individual emission sector.

The large proportion of black carbon (BC)-containing aerosols in the urban atmosphere

The accurate derivation of the proportion and absorption enhancement of black carbon (BC)-containing aerosols in the atmosphere is critical to assess their effect on air quality and climate. Here, using the field measured size-resolved volatility shrink factor, BC bulk mass concentration and the BC mass fraction in BC-containing particles in winter Beijing, we retrieved and quantified both the number and mass concentration of (1) non-BC, (2) internally mixed BC and (3) externally mixed BC of ambient fine aerosol particles. The reliability of the retrieval method has been evaluated by comparing with the simultaneously measured data. The number fraction of BC-containing particles accounts for 60-78% of ambient fine particles, with internally (both BC core and coating materials) and externally mixed BC of 51-64% and 9-23%, respectively. Only for nucleated particles on clean days, when nucleation is a major source of aerosol particles, did the non-BC component dominate (54%). A large amount of aerosols are BC-containing particles, with mass fraction of 32-52%, suggesting the dominant role of BC in elevating mass concentration of particulate matter (PM) in a polluted urban area. We also show that the BC particles are thickly coated with coating thickness (characterized by D_p/D_c, ratio of the BC diameter before and after heating at 300 °C) of 1.6-2.2, implying efficient aging of BC particles in polluted urban area. Our results imply a large proportion of BC-containing particles in the atmosphere, which could help towards understanding the role of BC on regional haze formation and climate forcing.

Aerosol optical properties and the mixing state of black carbon at a background mountainous site in Eastern China

In-situ measurements of aerosol optical properties were conducted at Mt. Huang from September 23 to October 28, 2012. Low averages of 82.2, 10.9, and 14.1 Mm^-1 for scattering coefficient (σ_{sp, neph, 550}), hemispheric backscattering coefficient (σ_{hbsp, neph, 550}), and absorption coefficient (σ_ap, 550), respectively, were obtained. Atmospheric aging process resulted in the increase of σ_ap, 550 but the decrease of the single scattering albedo (ω₅₅₀) at constant aerosol concentration. However, the proportion of non-light-absorbing components (non-BCs) was getting higher during the aging process, resulting in the increase of aerosol diameter, which also contributed to relatively higher σ_{sp, neph, 550} and ω₅₅₀. Diurnal cycles of σ_{sp, neph, 550} and σ_ap, 550 with high values in the morning and low values in the afternoon were observed closely related to the development of the planetary boundary layer and the mountain-valley breeze. BC mixing state, represented by the volume fraction of externally mixed BC to total BC (r), was retrieved by using the modified Mie model. The results showed r reduced from about 70% to 50% when the externally mixed non-BCs were considered. The periodical change and different diurnal patterns of r were due to the atmospheric aging and different air sources under different synoptic systems. Local biomass burning emissions were also one of the influencing factors on r. Aerosol radiative forcing for different mixing state were evaluated by a "two-layer-single-wavelength" model, showing the cooling effect of aerosols weakened with BC mixing state changing from external to core-shell mixture.

Modelling black carbon absorption of solar radiation: combining external and internal mixing assumptions

An accurate simulation of the absorption properties is key for assessing the radiative effects of aerosol on meteorology and climate. The representation of how chemical species are mixed inside the particles (the mixing state) is one of the major uncertainty factors in the assessment of these effects. Here we compare aerosol optical properties simulations over Europe and North America, coordinated in the framework of the third phase of the Air Quality Model Evaluation International Initiative (AQMEII), to 1 year of AERONET sunphotometer retrievals, in an attempt to identify a mixing state representation that better reproduces the observed single scattering albedo and its spectral variation. We use a single post-processing tool (FlexAOD) to derive aerosol optical properties from simulated aerosol speciation profiles, and focus on the absorption enhancement of black carbon when it is internally mixed with more scattering material, discarding from the analysis scenes dominated by dust. We found that the single scattering albedo at 440 nm (ω _0,440) is on average overestimated (underestimated) by 3-5 % when external (core-shell internal) mixing of particles is assumed, a bias comparable in magnitude with the typical variability of the quantity. The (unphysical) homogeneous internal mixing assumption underestimates ω _0,440 by ~ 14 %. The combination of external and core-shell configurations (partial internal mixing), parameterized using a simplified function of air mass aging, reduces the ω _0,440 bias to -1/-3 %. The black carbon absorption enhancement (E _abs) in core-shell with respect to the externally mixed state is in the range 1.8-2.5, which is above the currently most accepted upper limit of ~ 1.5. The partial internal mixing reduces E _abs to values more consistent with this limit. However, the spectral dependence of the absorption is not well reproduced, and the absorption Ångström exponent AAE 675 440 is overestimated by 70-120 %. Further testing against more comprehensive campaign data, including a full characterization of the aerosol profile in terms of chemical speciation, mixing state, and related optical properties, would help in putting a better constraint on these calculations.

Strong impact of wildfires on the abundance and aging of black carbon in the lowermost stratosphere

Unique information about the abundance and evolution of wildfire-emitted black carbon (BC) in the lowermost part of the stratosphere (LMS) was obtained from long-term airborne measurements made in cooperation with Lufthansa through the Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) project, part of the In-service Aircraft for a Global Observing System (IAGOS) framework. Our results demonstrate that wildfires can dramatically increase BC mass concentration in the LMS, substantially enhance regional climate forcing, and are a challenge for model simulations. Climate change is expected to increase the frequency and spread of wildfires. Thus, recording a present-day baseline with extensive and long-term measurements should help to constrain model estimations of the climate impact of BC and foster our fundamental understanding of future climate change.

Wildfires inject large amounts of black carbon (BC) particles into the atmosphere, which can reach the lowermost stratosphere (LMS) and cause strong radiative forcing. During a 14-month period of observations on board a passenger aircraft flying between Europe and North America, we found frequent and widespread biomass burning (BB) plumes, influencing 16 of 160 flight hours in the LMS. The average BC mass concentrations in these plumes (∼140 ng·m⁻³, standard temperature and pressure) were over 20 times higher than the background concentration (∼6 ng·m⁻³) with more than 100-fold enhanced peak values (up to ∼720 ng·m⁻³). In the LMS, nearly all BC particles were covered with a thick coating. The average mass equivalent diameter of the BC particle cores was ∼120 nm with a mean coating thickness of ∼150 nm in the BB plume and ∼90 nm with a coating of ∼125 nm in the background. In a BB plume that was encountered twice, we also found a high diameter growth rate of ∼1 nm·h⁻¹ due to the BC particle coatings. The observed high concentrations and thick coatings of BC particles demonstrate that wildfires can induce strong local heating in the LMS and may have a significant influence on the regional radiative forcing of climate.

Influence of aerosol hygroscopicity and mixing state on aerosol optical properties in the Pearl River Delta region, China

Both the effects of aerosol hygroscopicity and mixing state on aerosol optical properties were analyzed using ground-based measurements and a Mie model in this study. The sized-resolved particle hygroscopic growth factor at RH = 90% (Gf(90%)) and the enhancement factor for the scattering coefficients (f(RH)_sp) were measured by a self-constructed Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) and two nephelometers in parallel (PNEPs) respectively from 22nd February to 18th March 2014 in the Pearl River Delta, China. In addition, the particle number size distribution (PNSD) and BC mass concentration (M_BC) were measured simultaneously. During the observation period, the f(RH)_sp increased sharply along with increasing RH (40%-85%) and the value of f(80%)_sp was 1.77 ± 0.18. The mean Gf(90%) for all particles are 1.44 (80 nm), 1.48 (110 nm), 1.52 (150 nm) and 1.55 (200 nm), and the mean Gf(90%) for more-hygroscopic particles are 1.58 (80 nm), 1.63 (110 nm), 1.66 (150 nm) and 1.67 (200 nm) respectively. Based on Gf, PNSD and M_BC, the enhancement factor of the aerosol optical properties (extinction (f(RH)_ep), scattering (f(RH)_sp), backscattering (f(RH)_hbsp), absorption (f(RH)_absp), and hemispheric backscatter fraction (f(RH)_hbsp)) were calculated under three aerosol mixing state assumptions. The results show that the calculated f(80%)_sp values agreed well with the ones measured by PNEPs, illustrating that the Gf size distribution fittings are reasonable. The f(RH)_ep, f(RH)_sp and f(RH)_hbsp increased along with increasing RH for three mixtures, while f(RH)_HBF decreased. The f(RH)_absp increased for the homogenously internal mixture, but remained stable for the external mixture. For the core-shell mixture, the f(RH)_absp increased from RH = 0 to 75% and then decreased, due to a decrease of light entering the BC core. The enhancement factor of aerosol direct radiative forcing (f(RH)_Fr) increased sharply as the RH elevated for the external mixing state. However, f(RH)_Fr increased or decreased along with the elevated RH for the homogenously internal mixture and the core-shell mixture depending on initial value of the aerosol direct radiative forcing (∆F_r) in a dry condition.

Sources and Health Risks of Heavy Metals in PM2.5 in a Campus in a Typical Suburb Area of Taiyuan, North China

To evaluate air pollution and the public health burden of heavy metals in PM2.5 in a campus with a population of approximately 40,000 in a typical suburb area of Taiyuan, North China, PM2.5 measurements were conducted during the spring and winter of 2016. The average concentrations of PM2.5 in spring and winter were 97.3 ± 35.2 µg m−3 and 205.9 ± 91.3 µg m−3, respectively. The order of concentration of heavy metals in PM2.5 was as follows: Zn > Pb > Mn > Cu > Cr > Ni > Cd > As, in both spring and winter. The concentrations of Cd and Pb in winter and the concentrations of Cr in both spring and winter in this study were significantly higher than the corresponding air quality standard values. Road/soil dust, industrial emissions/coal combustion, and vehicle emissions/oil combustion and coal combustion/industrial emissions, road/soil dust, and vehicle emissions/oil combustion were identified by principal component analysis to be the major sources of heavy metals for spring and winter, respectively. The carcinogenic risks posed by Cr via the three exposure pathways (except for inhalation exposure to children) and by Pb via ingestion exposure exceeded the acceptable level for both children and adults. The non-carcinogenic risks posed by Mn via inhalation for both children and adults, and by Cr and Pb for children via ingestion exceeded the acceptable level.

Impact of size distributions of major chemical components in fine particles on light extinction in urban Guangzhou

To evaluate the impact of fine particulate matter (PM_2.5) size distribution on aerosol chemical and optical properties, dominant chemical components including water-soluble inorganic ions (WSII), organic carbon (OC) and elemental carbon (EC) in PM₁ and PM_2.5, aerosol scattering coefficient (b_sp), and aerosol absorption coefficient (b_ap) were collected synchronously at an urban site in Guangzhou, south China during a typical summer month in 2009 and a winter month in 2010. PM₁ (sizes smaller than 1μm) constituted 77% and 63% of PM_2.5 in summer and winter, respectively. From the reconstructed mass concentrations, the sum of SO₄^2-, NO₃^- and NH₄⁺ (SNA) distributed more in PM₁ than in PM_1-2.5 (PM_2.5 minus PM₁) in summer and the opposite was found in winter, while carbonaceous aerosols distributed more in PM₁ in both summer and winter. With the aggravation of PM_2.5 pollution, the mass fraction of PM₁/PM_2.5 increased for (NH₄)₂SO₄ (AS), NH₄NO₃ (AN) and EC but decreased for organic matter (OM) in summer, and the opposite was found in winter. B_sp of PM₁ and PM_1-2.5 was estimated from the mass extinction efficiencies (MSEs) of the dominant chemical components, which showed good correlations (R²=0.99) with measured ones and those estimated using the IMPROVE formula. The fractional contributions of dominant chemical components to extinction coefficient (b_ext) were consistent with their respective mass size distributions, indicating the importance of chemically-resolved aerosol size distributions on aerosol optical properties and haze formation.

A closure study of aerosol optical properties at a regional background mountainous site in Eastern China

There is a large uncertainty in evaluating the radiative forcing from aerosol-radiation and aerosol-cloud interactions due to the limited knowledge on aerosol properties. In-situ measurements of aerosol physical and chemical properties were carried out in 2012 at Mt. Huang (the Yellow Mountain), a continental background mountainous site in eastern China. An aerosol optical closure study was performed to verify the model outputs by using the measured aerosol optical properties, in which a spherical Mie model with assumptions of external and core-shell mixtures on the basis of a two-component optical aerosol model and high size-segregated element carbon (EC) ratio was applied. Although the spherical Mie model would underestimate the real scattering with increasing particle diameters, excellent agreement between the calculated and measured values was achieved with correlation coefficients above 0.98. Sensitivity experiments showed that the EC ratio had a negligible effect on the calculated scattering coefficient, but largely influenced the calculated absorption coefficient. The high size-segregated EC ratio averaged over the study period in the closure was enough to reconstruct the aerosol absorption coefficient in the Mie model, indicating EC size resolution was more important than time resolution in retrieving the absorption coefficient in the model. The uncertainties of calculated scattering and absorption coefficients due to the uncertainties of measurements and model assumptions yielded by a Monte Carlo simulation were ±6% and ±14% for external mixture and ±9% and ±31% for core-shell mixture, respectively. This study provided an insight into the inherent relationship between aerosol optical properties and physicochemical characteristics in eastern China, which could supplement the database of aerosol optical properties for background sites in eastern China and provide a method for regions with similar climate.

Megacities and large urban agglomerations in the coastal zone: interactions between atmosphere, land, and marine ecosystems

Megacities are not only important drivers for socio-economic development but also sources of environmental challenges. Many megacities and large urban agglomerations are located in the coastal zone where land, atmosphere, and ocean meet, posing multiple environmental challenges which we consider here. The atmospheric flow around megacities is complicated by urban heat island effects and topographic flows and sea breezes and influences air pollution and human health. The outflow of polluted air over the ocean perturbs biogeochemical processes. Contaminant inputs can damage downstream coastal zone ecosystem function and resources including fisheries, induce harmful algal blooms and feedback to the atmosphere via marine emissions. The scale of influence of megacities in the coastal zone is hundreds to thousands of kilometers in the atmosphere and tens to hundreds of kilometers in the ocean. We list research needs to further our understanding of coastal megacities with the ultimate aim to improve their environmental management.

Analysis of atmospheric aerosols

Aerosols represent an important component of the Earth's atmosphere. Because aerosols are composed of solid and liquid particles of varying chemical complexity, size, and phase, large challenges exist in understanding how they impact climate, health, and the chemistry of the atmosphere. Only through the integration of field, laboratory, and modeling analysis can we begin to unravel the roles atmospheric aerosols play in these global processes. In this article, we provide a brief review of the current state of the science in the analysis of atmospheric aerosols and some important challenges that need to be overcome before they can become fully integrated. It is clear that only when these areas are effectively bridged can we fully understand the impact that atmospheric aerosols have on our environment and the Earth's system at the level of scientific certainty necessary to design and implement sound environmental policies.