Evaluation of the Influence between Local Meteorology and Air Quality in Beijing Using Generalized Additive Models

Previous studies have confirmed the inextricable connection between meteorological factors and air pollutants. This study presents the complex nonlinear relationship between meteorological variables and four major air pollutants under high-concentration air pollution in Beijing. The generalized additive model combined with marginal effects is used for quantitative analysis. After controlling the confounding factors such as long-term trends, seasonality and spatio-temporal deviation, the final fitting results exhibit that temperature, relative humidity and visibility are the most significant meteorological variables associating with PM2.5 concentration, and the marginal effect reaches 80%, −23% and 270%, respectively. Temperature and relative humidity are the most significant variables for SO2, and the marginal effect reaches 15% and 7%. The most significant variables for O3 are temperature and solar radiation, with marginal effect of up to 70% and 8%. Atmospheric pressure and temperature results in a positive effect on CO, and the marginal effect can reach 18% and 80%. All these indicate that local meteorological variables are a significant driving factor for air quality in Beijing. Other variables, such as wind speed, visibility, and precipitation, display some influence on air pollutants, but have less explanatory power in the model. Overall, our study provides a better understanding of the relationship between local meteorological variables and air quality, as well as an insight into how climate change affects air quality.

SO2 measurements in a clean coastal environment of the southwestern Europe: Sources, transport and influence in the formation of secondary aerosols

Two years of SO₂ measurements at El Arenosillo observatory located in the Gulf of Cadiz (Atlantic Ocean) were investigated. Annual hourly averages of 1.9 ± 1.5 μg m^-3 and p95 between 3 and 4.4 μg m^-3 were recorded, showing clean and background environments. Monthly means vary between 1.5 and 2.4 μg m^-3, a monthly evolution was not found. SO₂ fields from the MERRA2 model were used to identify SO₂ sources and its transport, which could be affecting the studied region. Although SO₂ records were low, major conductive for SO₂ increases were observed in specific periods. A selection methodology was applied to extract these events, which showed a mean of ~11 μg m^-3. Surface meteorological observations and ERA5 meteorological fields from the ECMWF model were used to assess the weather conditions. SO₂ increases, in cold months occurred under conditions governed by synoptic-scale. Two types of transport scenarios were identified: SO₂ transport defined as direct impact, which is the sum of the plumes from Portugal and the Huelva area; and indirect impact, where SO₂ and sulphate particle emissions from Portugal were transported and accumulated in the Gulf of Cadiz and then carried inland, where new particle formation were observed. Episodes with high SO₂ concentrations were also reported in warm periods associated with pure sea-land breezes. The SO₂ peaks under sea-land breezes were associated with the transport of SO₂ from the south of Portugal to the Gulf of Cadiz, whereas SO₂ from the east of the Iberian Peninsula and north of Africa reached the Mediterranean Sea and were then transported to the Atlantic Ocean following the Strait of Gibraltar. Blocking of the airflows from the Mediterranean Sea to the Atlantic Ocean turns the Gulf of Cadiz into a chemical reservoir, where chemical species such as SO₂ can accumulate, triggering new particle formation processes.

Aerosol Liquid Water Promotes the Formation of Water-Soluble Organic Nitrogen in Submicrometer Aerosols in a Suburban Forest

Water-soluble organic nitrogen (WSON) affects the formation, chemical transformations, hygroscopicity, and acidity of organic aerosols as well as biogeochemical cycles of nitrogen. However, large uncertainties exist in the origins and formation processes of WSON. Submicrometer aerosol particles were collected at a suburban forest site in Tokyo in summer 2015 to investigate the relative impacts of anthropogenic and biogenic sources on WSON formations and their linkages with aerosol liquid water (ALW). The concentrations of WSON (ave. 225 ± 100 ngN m^-3) and ALW exhibited peaks during nighttime, which showed a significant positive correlation, suggesting that ALW significantly contributed to WSON formation. Further, the thermodynamic predictions by ISORROPIA-II suggest that ALW was primarily driven by anthropogenic sulfate. Our analysis, including positive matrix factorization, suggests that aqueous-phase reactions of ammonium and reactive nitrogen with biogenic volatile organic compounds (VOCs) play a key role in WSON formation in submicrometer particles, which is particularly significant in nighttime, at the suburban forest site. The formation of WSON associated with biogenic VOCs and ALW was partly supported by the molecular characterization of WSON. The overall result suggests that ALW is an important driver for the formation of aerosol WSON through a combination of anthropogenic and biogenic sources.

Recent changes of trans-boundary air pollution over the Yellow Sea: Implications for future air quality in South Korea

The influence of air pollutants originating from the Chinese region on air quality over South Korea has been a major concern for policymakers. To investigate the inter-annual trends of the long-distance transport of air pollutants from China to South Korea, multi-year trend analysis was carried out for Aerosol Optical Depth (AOD, as a proxy of particulate matter), and CO (a water-insoluble air pollutant) and SO₂ (a partially water-soluble air pollutant), over three regions in Northeast Asia. Air pollutants are typically long-range transported from the highly polluted parts of China to South Korea through the Yellow Sea. Taking advantage of this geographical merit, we carried out the multi-year trend analysis with a special focus on the Yellow Sea region. Decreasing trends of about 5-10%, 13-17% and 55-61% during the last decade were observed in surface CO, AOD and tropospheric SO₂ columns over the North China Plain (NCP), Yellow Sea (YS), and South Korea (SK), respectively. Such decreasing trends were also found consistently during the last three, five, and seven years, indicating that the changes in pollution levels are likely in response to recent policy measures taken by the Chinese and Korean governments to improve air quality over the regions. Due to these efforts, the amounts of air pollutants transported from China to South Korea are expected to decrease in future years, to the likely rates of 1.50 ppb yr^-1, 0.05 DU yr^-1, and 0.56 μg m^-3 yr^-1 over the YS region for CO, SO₂, and PM_2.5, respectively. Given the ambitious plans recently announced by the Chinese government for the 21st meeting of Conference of Parties (COP21) and its co-control effects, the suggested percentage rates may even be conservative numbers. This analysis is expected to provide South Korean policymakers with valuable information to establish new air pollution policies in South Korea.

Spatial and temporal variation in fine particulate matter mass and chemical composition: the Middle East Consortium for Aerosol Research Study

Ambient fine particulate matter (PM_2.5) samples were collected from January to December 2007 to investigate the sources and chemical speciation in Palestine, Jordan, and Israel. The 24-h PM_2.5 samples were collected on 6-day intervals at eleven urban and rural sites simultaneously. Major chemical components including metals, ions, and organic and elemental carbon were analyzed. The mass concentrations of PM_2.5 across the 11 sites varied from 20.6 to 40.3 μg/m³, with an average of 28.7 μg/m³. Seasonal variation of PM_2.5 concentrations was substantial, with higher average concentrations (37.3 μg/m³) in the summer (April–June) months compared to winter (October–December) months (26.0 μg/m³) due mainly to high contributions of sulfate and crustal components. PM_2.5 concentrations in the spring were greatly impacted by regional dust storms. Carbonaceous mass was the most abundant component, contributing 40% to the total PM_2.5 mass averaged across the eleven sites. Crustal components averaged 19.1% of the PM_2.5 mass and sulfate, ammonium, and nitrate accounted for 16.2%, 6.4%, and 3.7%, respectively, of the total PM_2.5 mass. The results of this study demonstrate the need to better protect the health and welfare of the residents on both sides of the Jordan River in the Middle East.

Ship-plume sulfur chemistry: ITCT 2K2 case study

The ship-plume sulfur chemistry was investigated for the ITCT 2K2 (Intercontinental Transport and Chemical Transformation 2002) ship-plume experiment, using the ship-plume photochemical/dynamic model developed in this study. In order to evaluate the performance of the model, the model-predicted mixing ratios of SO2 and H2SO4 were compared with those observed. From these comparisons, it was found that the model-predicted levels were in reasonable agreements with those observed (0.56≤R≤0.71), when the pH of sea-salt particles (pHss) was ≤~6.5. The ship-plume equivalent lifetimes of SO2 (τ(eq)(SO(2))) were also estimated/investigated for this particular ship-plume case. The magnitudes of τ(eq)(SO(2)) were found to be controlled by two main factors: (i) the mixing ratios of in-plume hydroxyl radicals (OH) and (ii) pHss. The former is governed primarily by stability conditions of the marine boundary layer (MBL), when the ship NOx emission rate is fixed. The latter determines if the heterogeneous oxidation of dissolved SO2 occurs via reaction with hydrogen peroxide (H2O2, when pHss<6.5) or with ozone (O3, when pHss>6.5). According to the multiple ship-plume photochemical/dynamic model simulations, the estimated τ(eq)(SO(2)) over the entire ship plumes ranged from 10.32 to 14.32 h under moderately stable (E) to stable (F) MBL conditions. These values were clearly shorter than the background SO2 lifetime (τ(b)(SO(2))) of 15.18-23.20 h. In contrast, τ(eq)(SO(2)) was estimated to be 0.33 h when the pHss remained at ~8.0 (a rather unlikely case). In addition, the SO2 loss budget was further analyzed to estimate the influences of the two main factors on the ship-plume sulfur chemistry. The changes in the loss budget with pHss clearly showed a shift in the dominant SO2 loss processes from heterogeneous SO2 conversion (when pHss>~6.5) to the gas-phase oxidation of SO2 by OH (when pHss<~6.5).

Tales of volcanoes and El-Nino southern oscillations with the oxygen isotope anomaly of sulfate aerosol

The ability of sulfate aerosols to reflect solar radiation and simultaneously act as cloud condensation nuclei renders them central players in the global climate system. The oxidation of S(IV) compounds and their transport as stable S(VI) in the Earth's system are intricately linked to planetary scale processes, and precise characterization of the overall process requires a detailed understanding of the linkage between climate dynamics and the chemistry leading to the product sulfate. This paper reports a high-resolution, 22-y (1980-2002) record of the oxygen-triple isotopic composition of sulfate (SO4) aerosols retrieved from a snow pit at the South Pole. Observed variation in the O-isotopic anomaly of SO4 aerosol is linked to the ozone variation in the tropical upper troposphere/lower stratosphere via the Ozone El-Niño Southern Oscillations (ENSO) Index (OEI). Higher (17)O values (3.3‰, 4.5‰, and 4.2‰) were observed during the three largest ENSO events of the past 2 decades. Volcanic events inject significant quantities of SO4 aerosol into the stratosphere, which are known to affect ENSO strength by modulating stratospheric ozone levels (OEI = 6 and (17)O = 3.3‰, OEI = 11 and (17)O = 4.5‰) and normal oxidative pathways. Our high-resolution data indicated that (17)O of sulfate aerosols can record extreme phases of naturally occurring climate cycles, such as ENSOs, which couple variations in the ozone levels in the atmosphere and the hydrosphere via temperature driven changes in relative humidity levels. A longer term, higher resolution oxygen-triple isotope analysis of sulfate aerosols from ice cores, encompassing more ENSO periods, is required to reconstruct paleo-ENSO events and paleotropical ozone variations.

Characterization of solvent-extractable organics in urban aerosols based on mass spectrum analysis and hygroscopic growth measurement

To characterize atmospheric particulate organics with respect to polarity, aerosol samples collected on filters in the urban area of Nagoya, Japan, in 2009 were extracted using water, methanol, and ethyl acetate. The extracts were atomized and analyzed using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a hygroscopicity tandem differential mobility analyzer. The atmospheric concentrations of the extracted organics were determined using phthalic acid as a reference material. Comparison of the organic carbon concentrations measured using a carbon analyzer and the HR-ToF-AMS suggests that organics extracted with water (WSOM) and ethyl acetate (EASOM) or those extracted with methanol (MSOM) comprise the greater part of total organics. The oxygen-carbon ratios (O/C) of the extracted organics varied: 0.51-0.75 (WSOM), 0.37-0.48 (MSOM), and 0.27-0.33 (EASOM). In the ion-group analysis, WSOM, MSOM, and EASOM were clearly characterized by the different fractions of the CH and CO(2) groups. On the basis of the hygroscopic growth measurements of the extracts, κ of organics at 90% relative humidity (κ(org)) were estimated. Positive correlation of κ(org) with O/C (r 0.70) was found for MSOM and EASOM, but no clear correlation was found for WSOM.